Crystalline salt forms of boc-d-arg-dmt-lys-(boc)-phe-nh2

ABSTRACT

Disclosed are various crystalline salt forms of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH 2 .

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 16/603,117, filed Oct. 4, 2019; which is the U.S. National Stage of International Patent Application No. PCT/US2018/025990, filed Apr. 4, 2018; which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 62/481,766, filed Apr. 5, 2017.

BACKGROUND

Through oxidative phosphorylation, mitochondria convert nutrients and oxygen into adenosine triphosphate (ATP), the chemical transporter of energy in most aerobic organisms. The electron transport chain (ETC) of the mitochondria represent the primary source of ATP, as well as a source of reactive oxygen species (ROS). Mitochondrial dysfunction in a cell results in less ATP production and, as a result, insufficient energy to maintain the cell. Such dysfunction also results in excessive ROS production, spiraling cellular injury, and ultimately apoptosis of the cell. Accordingly, mitochondrial dysfunction is a key element believed to be at the root of a variety of serious, debilitating diseases.

Natural antioxidants, such as coenzyme Q and vitamin E, have been shown to provide some protection of the cell from damage induced by the elevated ROS levels associated with mitochondrial dysfunction. However, antioxidants or oxygen scavengers have also been shown to reduce ROS to unhealthy levels and may not reach the ETC in sufficient concentrations to correct the mitochondrial imbalance. Therefore, there is a need for novel compounds that can selectively target the ETC, restore efficient oxidative phosphorylation, and thereby address mitochondrial disease and dysfunction.

SUMMARY

Disclosed are various crystalline salt forms of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a XRPD pattern of a hydrochloride salt of Compound I.

FIG. 2 depicts a XRPD pattern of a tosylate salt of Compound I.

FIG. 3 depicts a XRPD pattern of a mesylate salt of Compound I.

FIG. 4 depicts a XRPD pattern of an oxalate salt of Compound I.

FIG. 5 depicts a XRPD pattern of a L-tartaric acid salt of Compound I.

FIG. 6 depicts a XRPD pattern of a fumarate salt of Compound I.

FIG. 7 depicts a XRPD pattern of a benzoic acid salt of Compound I.

FIG. 8 depicts a XRPD pattern of a succinate salt of Compound I.

FIG. 9 depicts a XRPD pattern of a hydrochloride salt of Compound I crystallized from Methanol:2-Propanol (75%:25% v/v).

FIG. 10 depicts a XRPD pattern of a hydrochloride salt of Compound I crystallized from Methanol.

FIG. 11 depicts a XRPD pattern of a tosylate salt of Compound I crystallized from Acetone.

FIG. 12 depicts a XRPD pattern of a mesylate salt of Compound I crystallized from Acetone.

FIG. 13 depicts a XRPD pattern of an oxalate salt of Compound I crystallized from Acetone.

FIG. 14 depicts a XRPD pattern of a benzoate salt of Compound I crystallized from Methanol.

DETAILED DESCRIPTION

The present invention features salts of Compound I:

(I; Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂), wherein Boc- represents tert-butyl-O—C(O)—.

Compound I is a synthetic precursor of Compound II:

(II; MTP-131; D-Arg-DMT-Lys-Phe-NH₂) or a salt thereof. Compound II has been shown to affect the mitochondrial disease process by helping to protect organs from oxidative damage caused by excess ROS production, and to restore normal ATP production.

A crystalline form of a salt of Compound I can be used to modulate/improve the physicochemical properties of the compound, including but not limited to solid state properties (e.g., crystallinity, hygroscopicity, melting point, or hydration), pharmaceutical properties (e.g., solubility/dissolution rate, stability, or compatibility), as well as crystallization characteristics (e.g., purity, yield, or morphology).

In certain embodiments, the polymorph of the crystalline salt is characterized by X-ray powder diffraction (XRPD). θ represents the diffraction angle, measured in degrees. In certain embodiments, the diffractometer used in XRPD measures the diffraction angle as two times the diffraction angle θ. Thus, in certain embodiments, the diffraction patterns described herein refer to X-ray intensity measured against angle 2θ.

In certain embodiments, a crystalline salt of Compound (I) is not solvated (e.g., the crystal lattice does not comprise molecules of a solvent). In certain alternative embodiments, a crystalline salt of Compound (I) is solvated. In some cases, the solvent is water.

In one aspect, the invention features a crystalline form of Compound I which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in any one of FIGS. 9-14.

In another aspect, the invention features a crystalline form of Compound I which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) as shown in any one of Tables A-F.

The relative intensity, as well as the two theta value, of each peak in Tables A-F, as well as FIGS. 9-14, may change or shift under certain conditions, although the crystalline form is the same. One of ordinary skill in the art should be able readily to determine whether a given crystalline form is the same crystalline form as described in one of Tables A-F as well as FIGS. 9-14 by comparing their XRPD data.

In another aspect, the invention features a crystalline form of a hydrochloride salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in FIG. 9.

In yet another aspect, the invention features a crystalline form of a hydrochloride salt salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in Table A.

In another aspect, the invention features a crystalline form of a hydrochloride salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 3.8, 4.3, 9.8, 14.6, 18.0, 18.8, 20.9, and 22.7.

In another aspect, the invention features a crystalline form of a hydrochloride salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 3.8, 4.3, 6.5, 7.3, 9.8, 13.3, 14.2, 14.6, 16.1, 16.9, 18.0, 18.8, 19.1, 19.7, 20.1, 20.5, 20.9, 22.0, 22.7, 23.2, 24.0, 25.2, and 25.9.

In another aspect, the invention features a crystalline form of a hydrochloride salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in FIG. 10.

In yet another aspect, the invention features a crystalline form of a hydrochloride salt salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in Table B.

In another aspect, the invention features a crystalline form of a hydrochloride salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 3.7, 4.4, 6.6, 9.7, 14.8, 18.0, 18.5, 18.8, 19.1, 20.9, and 22.7.

In another aspect, the invention features a crystalline form of a hydrochloride salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 3.7, 4.4, 6.6, 7.4, 9.7, 10.6, 13.2, 14.1, 14.8, 16.7, 18.0, 18.5, 18.8, 19.1, 19.5, 19.8, 20.1, 20.6, 20.9, 21.3, 22.0, 22.7, 23.1, and 24.0.

In yet another aspect, the invention features a crystalline form of a tosylate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in FIG. 11.

In yet another aspect, the invention features a crystalline form of a tosylate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in Table C.

In another aspect, the invention features a crystalline form of a tosylate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 5.2, 8.9, 14.4, 17.3, 18.8, 19.5, and 21.0.

In another aspect, the invention features a crystalline form of a tosylate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 5.2, 8.9, 10.8, 13.4, 14.4, 16.0, 17.3, 18.8, 19.5, 21.0, 23.3, and 24.6.

In yet another aspect, the invention features a crystalline form of a mesylate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in FIG. 12.

In yet another aspect, the invention features a crystalline form of a mesylate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in Table D.

In another aspect, the invention features a crystalline form of a mesylate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 5.4, 13.4, 14.8, 15.8, 17.6, 19.0, and 21.3.

In another aspect, the invention features a crystalline form of a mesylate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 5.4, 10.8, 13.4, 14.8, 15.8, 17.6, 19.0, 19.7, 21.3, 22.3. 24.1, and 25.7.

In yet another aspect, the invention features a crystalline form of an oxalate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in FIG. 13.

In yet another aspect, the invention features a crystalline form of an oxalate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in Table E.

In another aspect, the invention features a crystalline form of an oxalate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 7.8, 10.1, 12.8, 17.8, 18.5, 19.9, and 22.3.

In another aspect, the invention features a crystalline form of an oxalate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 4.1, 7.2, 7.8, 8.1, 10.1, 12.0, 12.8, 13.3, 14.5, 14.9, 17.8, 18.1. 18.5, 19.9, 20.4, 21.9, 22.0, 22.3, and 23.5.

In yet another aspect, the invention features a crystalline form of a benzoate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in FIG. 14.

In yet another aspect, the invention features a crystalline form of a benzoate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in Table F.

In another aspect, the invention features a crystalline form of a benzoate of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 3.7, 4.4, 14.1, 18.1, 18.9, 20.7, 22.3, and 24.3.

In another aspect, the invention features a crystalline form of a benzoate salt of Compound I, which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) of 3.7, 4.4, 6.7, 9.9, 13.3, 13.7, 14.1, 15.8, 17.2, 18.1, 18.4, 18.9, 19.5, 20.7, 20.9, 21.6, 22.3, and 24.3.

The term “substantially pure” as used herein, refers to a crystalline polymorph that is greater than 90% pure, meaning that contains less than 10% of any other compound, including the corresponding amorphous compound or an alternative polymorph of the crystalline salt. Preferably, the crystalline polymorph is greater than 95% pure, or even greater than 98% pure.

In one embodiment, the present invention features a crystalline form of Compound I which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern as shown in any one of FIGS. 1-8 and which is substantially pure. For example, the crystalline form can be at least 90% pure, preferably at least 95% pure, or more preferably at least 98% pure.

In another embodiment, the present invention features a crystalline form of Compound I which has characteristic peaks in the X-ray powder diffraction (XRPD) pattern at values of two theta (° 2θ) as shown in any one of Tables 1-8 and which is substantially pure. For example, the crystalline form can be at least 90% pure, preferably at least 95% pure, or more preferably at least 98% pure.

In another aspect, the invention relates to preparing compound (II) or a salt thereof (e.g., the tri-HCl salt) from compound (I). In some embodiments, the compound (II) is obtained via deprotection of a crystalline form of compound (I). In some embodiments, the deprotection comprises preparing a mixture (e.g., a slurry) of a crystalline form of compound (I) and a scavenger in a solvent. In some embodiments, the scavenger is triisopropylsilane. In some embodiments the solvent is 2,2,2-trifluoroethanol. In some embodiments, the deprotection further comprises addition of an acid. In some embodiments, the acid is concentrated hydrochloric acid (e.g., 5-6 M HCl).

Methods of Making the Crystalline Salts

In certain embodiments, the invention relates to a method for the preparation of a crystalline salt of compound (I), comprising a) providing a freebase mixture of compound (I) in a first organic solvent; b) contacting the freebase mixture with a reagent solution comprising an acid and optionally a second organic solvent under conditions sufficient to form a mixture comprising a salt of compound (I); and c) crystallizing the salt of compound (I) from the mixture comprising the salt of compound (I).

In certain embodiments, the invention relates to a method for the preparation of a crystalline salt of compound (I), comprising a) providing a first salt mixture of compound (I) in a first organic solvent; b) contacting the first salt mixture with a reagent solution comprising an acid and optionally a second organic solvent under conditions sufficient to form a mixture comprising a second salt of compound (I); and c) crystallizing the second salt of compound (I) from the mixture comprising the second salt of compound (I).

In certain embodiments, the invention relates to a method for the preparation of a crystalline salt of a compound having the structure of formula (II), comprising a) providing a first mixture comprising a protected form of compound (I) in a first organic solvent; b) contacting the first mixture with a reagent solution comprising an acid and optionally a second organic solvent under conditions sufficient to deprotect the protected form of compound (I) and to form a mixture comprising a salt of compound (II); and c) crystallizing the salt of compound (II) from the mixture comprising the salt of compound (II). In certain embodiments, the mixture comprising a salt of compound (I) formed in step b) is a solution. In certain embodiments, the mixture formed in step b) is a slurry or a suspension.

In certain embodiments, the mixture comprising the salt of compound (I) or (II) is a solution, and the step of crystallizing the salt from the mixture comprises bringing the solution to supersaturation to cause the salt of compound (I) or (II) to precipitate out of solution.

In certain embodiments, bringing the mixture comprising the salt of compound (I) or (II) to supersaturation comprises the slow addition of an anti-solvent, such as heptanes, hexanes, ethanol, or another polar or non-polar liquid miscible with the organic solvent, allowing the solution to cool (with or without seeding the solution), reducing the volume of the solution, or any combination thereof. In certain embodiments, bringing the mixture comprising the salt of compound (I) or (II) to supersaturation comprises adding an anti-solvent, cooling the solution to ambient temperature or lower, and reducing the volume of the solution, e.g., by evaporating solvent from the solution. In certain embodiments, allowing the solution to cool may be passive (e.g., allowing the solution to stand at ambient temperature) or active (e.g., cooling the solution in an ice bath or freezer).

In certain embodiments, the preparation method further comprises isolating the salt crystals, e.g. by filtering the crystals, by decanting fluid from the crystals, or by any other suitable separation technique. In further embodiments, the preparation method further comprises washing the crystals.

In certain embodiments, the preparation method further comprises inducing crystallization. The method can also comprise the step of drying the crystals, for example under reduced pressure. In certain embodiments, inducing precipitation or crystallization comprises secondary nucleation, wherein nucleation occurs in the presence of seed crystals or interactions with the environment (crystallizer walls, stirring impellers, sonication, etc.).

In certain embodiments, the freebase mixture of compound (I) in a first organic solvent is a slurry. In certain embodiments, the freebase mixture of compound (I) in a first organic solvent is a solution.

In certain embodiments, the first organic solvent and the second organic solvent, if present, comprise acetone, anisole, methanol, 1-butanol, 2-butanone, iso-butanol, tert-butanol, sec-butanol, cyclopentyl methyl ether (CPME), benezotrifluoride (BTF), 1-propanol, 2-propanol (IPA), water, dichloromethane, anisole, acetonitrile, ethylene glycol, tert-butyl methyl ether (t-BME), DMSO, ethylene glycol, toluene, tetrahydrofuran (THF), heptane, acetonitrile, N,N-dimethylacetamide (DMA), dimethylformamide (DMF), dimethylsulfoxide (DMSO), 1,4-dioxane, 2-ethoxy ethanol, heptane, isopropyl acetate, methyl acetate, 2-methyl THF, methyl isobutyl ketone (MIBK), 1-propanol, ethanol, ethyl acetate, hexanes, methyl acetate, isopropyl acetate, methylethyl ketone, 1,4-dioxane, methyl cyclohexane, N-methyl-2-pyrrolidone (NMP), or any combination thereof.

In certain embodiments, the first organic solvent and the second organic solvent, if present, are the same. In alterative embodiments, the first organic solvent and the second organic solvent, if present, are different.

In certain embodiments, washing the crystals comprises washing with a liquid selected from anti-solvent, acetonitrile, ethanol, heptanes, hexanes, methanol, tetrahydrofuran, toluene, water, or a combination thereof. As used herein, “anti-solvent” means a solvent in which the salt crystals are insoluble, minimally soluble, or partially soluble. In practice, the addition of an anti-solvent to a solution in which the salt crystals are dissolved reduces the solubility of the salt crystals in solution, thereby stimulating precipitation of the salt. In certain embodiments, the crystals are washed with a combination of anti-solvent and the organic solvent. In certain embodiments, the anti-solvent is water, while in other embodiments it is an alkane solvent, such as hexane or pentane, or an aromatic hydrocarbon solvent, such as benzene, toluene, or xylene. In certain embodiments, the anti-solvent is ethanol.

In certain embodiments, washing the crystals comprises washing crystalline compound (I) with a solvent or a mixture of one or more solvents, which are described above. In certain embodiments, the solvent or mixture of solvents is cooled prior to washing.

The invention now being generally described, it will be more readily understood by reference to the following examples which are included merely for purposes of illustration of certain aspects and embodiments of the present invention, and are not intended to limit the invention.

EXAMPLES Materials and Methods

X-Ray Powder Diffraction (XRPD)

Powder x-ray diffraction experiments were performed on a PANalytical X'Pert Pro X-ray Diffractometer, scanning the samples between 3 and 35°2θ. Material was loaded into a 96-well plate with mylar film as the base. The samples were then loaded into the plate holder of a PANalytical X'Pert Pro X-ray Diffractometer running in transmission mode and analyzed, using the following experimental conditions:

Raw Data Origin: XRPD measurement (*.XRPDML)

Scan Axis: Gonio

Start Position [° 2θ]: 3.0066

End Position [° 2θ]: 34.9866

Step Size [° 2θ]: 0.0130

Scan Step Time [s]: 18.8700

Scan Type: Continuous

PSD Mode: Scanning

PSD Length [° 2θ]: 3.35

Offset [° 2θ]: 0.0000

Divergence Slit Type: Fixed

Divergence Slit Size [° ]: 1.0000

Specimen Length [mm]: 10.00

Measurement Temperature [° C.]: 25.00

Anode Material: Cu

K-Alpha1 [Å]: 1.54060

K-Alpha2 [Å]: 1.54443

K-Beta [Å]: 1.39225

K-A2/K-A1 Ratio: 0.50000

Generator Settings: 40 mA, 40 kV

Diffractometer Type: 0000000011154173

Diffractometer Number: 0

Goniometer Radius [mm]: 240.00

Dist. Focus-Diverg. Slit [mm]: 91.00

Incident Beam Monochromator: No

Spinning: No

Polarized Light Microscopy (PLM)

The presence of birefringence was determined using an Olympus BX50 polarizing microscope, equipped with a Motic camera and image capture software (Motic Images Plus 2.0). All images were recorded using the 20×objective, unless otherwise stated.

Thermogravimetric/Differential Thermal Analysis (TG/DTA)

Approximately 5 mg of material was weighed into an open aluminium pan and loaded into a simultaneous thermogravimetric/differential thermal analyzer (TG/DTA) and held at room temperature. The sample was then heated at a rate of 10° C./min from 20° C. to 300° C. during which time the change in sample weight was recorded along with any differential thermal events (DTA). Nitrogen was used as the purge gas, at a flow rate of 300 cm³/min.

Differential Scanning Calorimetry (DSC)

Approximately 5 mg of material was weighed into an aluminium DSC pan and sealed non-hermetically with a pierced aluminium lid. The sample pan was then loaded into a Seiko DSC6200 (equipped with a cooler) and held at 20° C. Once a stable heat-flow response was obtained, the sample and reference were heated to ca. 180° C. at a scan rate of 10° C./min and the resulting heat flow response monitored. Nitrogen was used as the purge gas, at a flow rate of 50 cm3/min.

Karl Fischer Coulometric Titration (KF)

Approximately 10 mg of solid material was accurately weighed into a vial. The solid was then dissolved in ca. 1 mL or 5 mL of pre-titrated Hydranal solution, sonicating for ca. 5-10 min. The solution was manually introduced into the titration cell of a Mettler Toledo C30 Compact Titrator and the weight of the solid entered on the instrument.

1H Nuclear Magnetic Resonance Spectroscopy (1H NMR)

1H-NMR spectroscopic experiments were performed on a Bruker AV500 (frequency: 500 MHz). Experiments were performed in d6-dimethylsulfoxide and each sample was prepared to ca. 10 mM concentration.

Gravimetric Vapour Sorption (GVS)

Approximately 15 mg of sample was placed into a mesh vapour sorption balance pan and loaded into an IGASorp Moisture Sorption Analyser balance by Hiden Analytical. The sample was subjected to a ramping profile from 40-90% relative humidity (RH) at 10% increments, maintaining the sample at each step until a stable weight had been achieved (98% step completion). After completion of the sorption cycle, the sample was dried using the same procedure to 0% RH, then subjected to a second ramping profile from 0-90% relative humidity. After completion of the second sorption cycle, the sample was dried using the same procedure to 0% RH, and finally taken back to the starting point of 40% RH. The weight change during the sorption/desorption cycles were plotted, allowing for the hygroscopic nature of the sample to be determined.

High Performance Liquid Chromatography-Ultraviolet Detection (HPLC-UV)

Column: Aeris Peptide C18 3.6 μm 250×4.6 mm column

Mobile Phase A: 0.05% TFA in deionized water

Mobile Phase B: 0.05% TFA in acetonitrile

Diluent: Water:Acetonitrile (90:10 v/v)

Flow Rate: 1.0 mL/min

-   -   Runtime: 32 minutes     -   Column Temperature: 30° C.     -   Autosampler Temperature: 5° C.     -   Injection Volume: 30 μL     -   Detection: 220 nm     -   Sample Concentration: 0.5 mg/mL

Gradient Program:

Time/min Solvent B (%) 0.00 5 15.00 25 20.00 50 25.00 90 27.00 90 27.10 5 32.00 5

Example 1. Experimental Approximate Solubility Assessment of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂

The solubility screen was carried out as follows:

-   -   Approximately 20 mg of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ was         weighed out into each vial.     -   Each solvent/solvent mixture was added to the appropriate vial         in 5 volume aliquots (100 μL).     -   In between additions, the sample was stirred at 50° C. (35° C.         for DCM).     -   If 2000 μL of solvent was added without dissolution of the         material, solubility was calculated to be below this point.     -   XRPD analysis of residual solids was carried out where         solubility was <17 mg/mL.

TABLE 1 Solvent Systems Selected for Solubility Screen Solvent ICH Class Acetone 3 Ethanol 3 Methanol 2 2-Propanol 3 2-Butanol 3 Methyl ethyl ketone 3 Dichloromethane* 2 Toluene 3 Acetone:water (50:50% v/v) 3 Ethanol:water (50:50% v/v) 3 Methanol:water (50:50% v/v) 2 2-propanol:water (50:50% v/v) 3 Tetrahydrofuran 2 Ethyl acetate 3 Acetonitrile 2 Trifluoroethanol Not classified Acetonitrile:water(50:50% v/v) 2 DMSO:acetone(50:50% v/v) 3 DMSO:water(50:50% v/v) 3

Small-Scale Crystallization Trials

Cooling/Temperature Cycling Crystallizations

General Procedure:

-   -   ca. 40 mg of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ was weighed out into         a 2 mL vial.     -   Respective solvent was added to the appropriate vial at ambient         (ca. 22° C.).     -   The experiments were heated to 50° C. and further stirred at 50°         C.     -   The experiments were stirred at 50° C. for ca. 1 hour.     -   The experiments were cooled down to 5° C. at 0.1° C./minutes.     -   The experiments were temperature cycled between 5° C. and 40° C.         for about 16 hours of cycling.     -   For the experiments where a slurry was observed, the solid was         isolated by centrifugation using a 0.22 μm Nylon polypropylene         centrifuge filter at 5° C. and the isolated material was         analyzed by XRPD.     -   The isolated material was dried under vacuum at ca. 30-40° C.         for ca. 18 hours.

TABLE 2 Experimental Details for Small-Scale Cooling/Temperature Cycling Crystallization Trials Vol. of Input Solvent/ solvent/ Concen- Sample Material solvent solvent system tration ID (mg) system used (mL) (mg/mL) 1 40.07 Acetone:water 0.60 66.8 (50:50% v/v) 2 40.64 Ethanol 0.40 101.6 3 41.51 Methanol 0.28 150.4 4 40.13 Methanol 0.40 100.3 5 41.23 Trifluoroethanol 0.10 412.3 6 40.40 Acetonitrile:water 0.27 149.6 (50:50% v/v) 7 40.12 DMSO:water(80:20% 0.20 200.6 v/v)

Anti-Solvent Addition/Cooling/Temperature Cycling Crystallizations

General Procedure:

-   -   ca. 40 mg of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ was weighed out into         a 2 mL vial.     -   Respective solvent was added to the appropriate vial at ambient         (ca. 22° C.).     -   The experiments were heated to 50° C. and further stirred at 50°         C.     -   A clear solution was observed at 50° C. for each experiment.     -   The respective anti-solvent was added to the appropriate         experiment at 50° C.     -   The experiments were stirred at 50° C. for ca. 1 hour.     -   The experiments were cooled down to 5° C. at 0.1° C./minutes.         The experiments were temperature cycled between 5° C. and 40° C.         for about 16 hours of cycling.     -   In the experiments where a thick slurry/thick precipitation was         observed, the respective solvent/anti-solvent (same ratio) was         added to improve mixing at 5° C.     -   For the experiments where a slurry was observed, the solid was         isolated by centrifugation using a 0.22 μm Nylon polypropylene         centrifuge filter at 5° C. and the isolated material was         analyzed by XRPD.

TABLE 3 Experimental Details for Anti-solvent addition Cooling/Temperature Cycling Crystallizations Vol. of Vol. of solvent Anti- Input system solvent Total Concen- % Sample Solid Solvent/ Anti- used used Volume tration % Anti- ID (mg) solvent system solvent (mL) (mL) (mL) (mg/mL) Solvent Solvent 1 41.63 Methanol Acetonitrile 0.28 0.1 0.38 110.7 73.4 26.6 2 41.08 Methanol EA 0.28 0.1 0.38 108.1 73.7 26.3 3 40.92 Methanol THF 0.28 0.1 0.38 107.7 73.7 26.3 4 40.5 Methanol Acetone 0.28 0.1 0.38 106.6 73.7 26.3 5 40.15 Methanol MEK 0.28 0.1 0.38 105.7 73.7 26.3 6 39.99 Methanol Toluene 0.28 0.1 0.38 105.2 73.7 26.3 7 40.16 Methanol Heptane 0.28 0.1 0.38 105.7 73.7 26.3 8 41.2 Ethanol EA 0.29 0.1 0.39 105.6 74.4 25.6 9 41.075 Ethanol THF 0.29 0.1 0.39 105.3 74.4 25.6 10 42.93 Ethanol Acetone 0.29 0.1 0.39 110.1 74.4 25.6 11 41.005 Ethanol MEK 0.29 0.1 0.39 105.1 74.4 25.6 12 40.78 Ethanol Toluene 0.29 0.1 0.39 104.6 74.4 25.6 13 42.045 Ethanol Heptane 0.29 0.1 0.39 107.8 74.4 25.6 14 39.295 Ethanol TBME 0.29 0.1 0.39 100.8 74.4 25.6 15 41.6 Ethanol Acetonitrile 0.29 0.1 0.39 106.7 74.4 25.6 16 40.16 Trifluoroethanol EA 0.1 0.1 0.2 200.8 50.0 50.0 17 40.095 Trifluoroethanol THF 0.1 0.1 0.2 200.5 50.0 50.0 18 42.545 Trifluoroethanol Acetone 0.1 0.1 0.2 212.7 50.0 50.0 19 41.175 Trifluoroethanol MEK 0.1 0.1 0.2 205.9 50.0 50.0 20 41.365 Trifluoroethanol Toluene 0.1 0.1 0.2 206.8 50.0 50.0 21 39 Trifluoroethanol Heptane 0.1 0.1 0.2 195.0 50.0 50.0 22 40.2 Trifluoroethanol TBME 0.1 0.1 0.2 201.0 50.0 50.0 23 41.48 Trifluoroethanol Acetonitrile 0.1 0.1 0.2 207.4 50.0 50.0

Anti-Solvent Addition Crystallizations

General Procedure:

-   -   ca. 40 mg of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ was weighed out into         a 2 mL vial.     -   Respective solvent was added to the appropriate vial at ambient         (ca. 22° C.).     -   The experiments were heated to 50° C. and stirred at 50° C.     -   Clear solution was observed at 50° C. for each experiment.     -   For addition of anti-solvent at 5° C.:         -   The experiments were cooled down to 5° C. at 0.1° C./minutes             and temperature cycled between 5° C. to 40° C. at 0.1°             C./minutes for ca. 18 hours cycle.         -   At 5° C., respective anti-solvent was added to the             appropriate experiment.         -   Further the experiments were stirred at 5° C. for ca 2             hours.     -   For anti-solvent addition at 50° C.:         -   To the clear solutions at 50° C., respective anti-solvents             were added.         -   The experiments were stirred at 50° C. for ca. 2 hours.         -   The experiments were cooled down to 5° C. at 0.1°             C./minutes. The experiments were temperature cycled between             5° C. and 40° C. for about 18 hour cycles.     -   In the experiments where a thick slurry/thick precipitation was         observed, the respective solvent/anti-solvent (same ratio) was         added to ensure a stirrable slurry at 5° C.     -   For the experiments where a flowable slurry was observed, the         solid was isolated by centrifugation using 0.22 μm Nylon         polypropylene centrifuge tube at 5° C. and the isolated material         was analyzed by XRPD.     -   The isolated material was dried under vacuum at 40° C. for ca.         24 hours.

TABLE 4 Experiment Details for Anti-Solvent Addition Crystallizations Vol. of Vol. of solvent Anti- Input Solvent/ system solvent Total Concen- % Sample Material solvent Anti- used used Volume tration % Anti- ID (mg) system solvent Temperature (mL) (mL) (mL) (mg/mL) Solvent Solvent  1 39.83 Methanol Acetonitrile 50° C. 0.27 0.81 1.08 36.9 25 75  2 39.61 EA 0.27 0.81 1.08 36.7 25 75  3 39.48 THE 0.27 0.81 1.08 36.6 25 75  4 40.49 Acetone 0.27 0.81 1.08 37.5 25 75  5 39.8  MEK 0.27 0.81 1.08 36.9 25 75  6 40.35 Toluene 0.27 0.81 1.08 37.4 25 75  7 40.53 TBME 0.27 0.81 1.08 37.5 25 75  8 39.51 Ethanol Acetonitrile 50° C. 0.29 0.87 1.16 34.1 25 75  9 41.04 EA 0.29 0.87 1.16 35.4 25 75 10 41.18 THE 0.29 0.87 1.16 35.5 25 75 11 42.05 Acetone 0.29 0.87 1.16 36.3 25 75 12 40.1  MEK 0.29 0.87 1.16 34.6 25 75 13 41.31 Toluene 0.29 0.87 1.16 35.6 25 75 14 41.27 TBME 0.29 0.87 1.16 35.6 25 75 15 39.7  Heptane 0.29 0.87 1.16 34.2 25 75 16 40.69 Methanol Acetonitrile  5° C. 0.27 0.81 1.08 37.7 25 75 17 40.82 EA 0.27 0.81 1.08 37.8 25 75 18 41.28 THE 0.27 0.81 1.08 38.2 25 75 19 40.29 Acetone 0.27 0.81 1.08 37.3 25 75 20 39.35 MEK 0.27 0.81 1.08 36.4 25 75 21 40.74 Toluene 0.27 0.81 1.08 37.7 25 75 22 41.68 TBME 0.27 0.81 1.08 38.6 25 75 23 40.96 Ethanol Acetonitrile  5° C. 0.29 0.87 1.16 35.3 25 75 24 40.33 EA 0.29 0.87 1.16 34.8 25 75 25 41.12 THE 0.29 0.87 1.16 35.4 25 75 26 39.97 Acetone 0.29 0.87 1.16 34.5 25 75 27 40.31 MEK 0.29 0.87 1.16 34.7 25 75 28 40.85 Toluene 0.29 0.87 1.16 35.2 25 75 29 40.72 TBME 0.29 0.87 1.16 35.1 25 75 30 39.7  Heptane 0.29 0.87 1.16 34.2 25 75

Seeded Cooling Crystallizations Using Solvent/Anti-Solvent Mixtures

General Procedure:

-   -   ca. 40 mg of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ was weighed out into         a 2 mL vial.     -   Respective solvent was added to the appropriate vial at ambient.     -   The experiments were heated to 50° C. and further stirred at 50°         C.         -   A clear solution was observed at 50° C. for each experiment.     -   The respective anti-solvent was added to the appropriate         experiment at 50° C. Clear solution was observed. The         experiments were seeded using crystalline Form 1.         -   Seed persisted in all the crystallizations and turbidity was             observed.     -   The experiments were stirred at 50° C. for ca. 1 hour.         -   Further nucleation was observed in every experiment.     -   The experiments were cooled down to 5° C. at 0.1° C./minute. The         experiments were further stirred at 5° C.     -   In the experiments where a thick slurry/thick precipitation was         observed, the respective solvent/anti-solvent (same ratio) was         added to improve mixing at 5° C.     -   The experiments were isolated by centrifugation using a 0.22 μm         Nylon polypropylene centrifuge filter at 5° C. and the isolated         material was analyzed by XRPD.     -   Dried under vacuum at 35° C. to 40° C. for ca. 24 hours.

TABLE 5 Experimental Details for Seeded Cooling Crystallizations using Solvent/Anti-solvent Mixtures Vol. of Vol. of Anti- % anti- Input solvent solvent Total Concen- solvent/ Sample Material Anti- used used Volume tration % co- ID (mg) Solvent solvent (mL) (mL) (mL) (mg/mL) Solvent solvent 1 40.3  Methanol Acetone 0.27 0.090 0.360 111.9 75 25 2 40   Methanol 2-propanol 0.27 0.090 0.360 111.1 75 25 3 39.9  Methanol 2-butanol 0.27 0.090 0.360 110.8 75 25 4 41.5  Methanol TBME 0.27 0.090 0.360 115.3 75 25 5 42.05 Methanol Ethanol 0.20 0.200 0.400 105.1 50 50 6 41.5  Ethanol 2-propanol 0.29 0.097 0.387 107.3 75 25 7 39.9  Ethanol 2-butanol 0.29 0.097 0.387 103.2 75 25

Scale-up Seeded Cooling Crystallizations Using Solvent/Anti-Solvent Mixture

In order to reproduce the most promising small-scale crystallizations, to assess repeatability and obtain further material for characterization, scale-up crystallizations were carried out. The following procedure was used:

-   -   ca. 250 mg of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ was weighed out         into a 20 mL scintillation vial.     -   Respective solvent was added to the appropriate vial at ambient.     -   The experiments were heated to 50° C. and further stirred at 50°         C.         -   A clear solution was observed at 50° C. for each experiment.     -   The respective anti-solvent was added to the appropriate         experiment at 50° C. Clear solution was observed. The         experiments were seeded using crystalline Form 1.         -   Seed persisted in all the crystallizations and turbidity was             observed.     -   The experiments were stirred at 50° C. for ca. 1 hour.     -   Further nucleation was observed in every experiment.     -   The experiments were cooled down to 5° C. at 0.1° C./minutes.         The experiments were further stirred at 5° C.     -   The experiments were isolated at 5° C. by filtering over a         Buchner funnel using Whatmann filter paper (Grade 597).     -   The isolated material from each batch was air dried for ca. 18         hours and further dried under vacuum at 35° C. to 40° C. for ca.         24 hours.

TABLE 6 Experimental Details for Scale-up Seeded Cooling Crystallizations Concen- Vol. of Concen- tration Vol. of Anti- tration Input in solvent solvent Total after % Sample Material Anti- solvent used used Volume ASA % Anti- ID (mg) Solvent solvent (mg/mL) (mL) (mL) (mL) (mg/mL) Solvent solvent 1 254 Methanol 100 2.543 2.543 100.00  100 2 250 Methanol Acetonitrile 150 1.667 0.556 2.222 112.50   75 25 3 256 Methanol THF 150 1.708 5.125 6.834 37.50  25 75 4 252 Ethanol Acetone 140 1.804 5.412 7.216 35.00  25 75

Primary Salt Screening

General Procedure

-   -   ca. 25 mg of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ was weighed out into         a 2 mL vial.     -   Respective solvent was added to the appropriate vial at ambient.     -   The experiments were stirred at 50° C. for ca. 1 hour.         -   For experiments using acetone as a solvent, a slurry was             observed.         -   For all other solvents, initially clear solutions were             observed but during further stirring at 50° C. precipitation             were observed. A slurry was present.     -   Further respective solvent was added to the appropriate         experiments either to dissolve the precipitated material or to         improve stirring.     -   The counterions were weighed (1.0 mole equivalent). To the vials         containing counterion, the respective solvent was added at         ambient.     -   The solution/slurry of counterion in the respective solvent         system was added to the appropriate vial containing the         slurry/clear solution of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ in the         respective solvent system at 50° C.     -   The vial containing solution/slurry of counterion was washed         with the respective solvent (50 μL) and the washings were added         to the salt formation reaction.     -   The experiments were stirred at 50° C. for ca. 1 hour.     -   In the experiments where a thick slurry was observed, the         respective solvent was added to improve mixing.     -   The experiments were cooled down to 5° C. at 0.1° C./minutes.         The experiments were temperature cycled between 5° C. and 40° C.         for ca. 16 hours of cycling.         -   At 16 hours, observations were recorded.         -   Temperature cycling was continued for a total of ca. 40             hours.         -   For the experiments where a slurry was observed, the solid             was isolated by centrifugation using a 0.22 μm Nylon             polypropylene centrifuge filter at 5° C. The isolated             material was dried under vacuum at 30° C. for 2 hours.         -   The isolated material was analyzed by XRPD.

TABLE 7 Experimental Details for Primary Salt Screening Further solvent system added Further either to solvent Solvent dissolve Solvent system Mass of Mass of added Initial or to system added to Input Solvent/ counter- to input concen- make for improve Sample Material solvent Counter- ion (mg material tration slurry counter- mixing ID (mg) system ion or μL) (μL) (mg/mL) (μL) ion (μL) (μL)  1 26.26 Acetone HC1 2.7 600 43.77 N/A 75 100  2 25.5  Acetonitrile: 2.6 130 196.15  25 50 100 water (50:50% v/v)  3 26.18 Ethanol 2.6 187 140.00  50 50 N/A  4 26.53 Methanol 2.7 132 200.98  75 50 N/A  5 25.38 Acetone  5.93 400 63.45 N/A 75 N/A  6 25.23 Acetonitrile: P-toluene  5.97 130 194.08  25 50 N/A water sulfonic (50:50% v/v) acid  7 25.33 Ethanol  6.06 187 135.45  50 50 N/A  8 25.53 Methanol  5.99 132 193.41  75 50 N/A  9 26.04 Acetone 2   400 65.10 N/A 75 N/A 10 25.5  Acetonitrile: Methane 2   130 196.15  25 50 N/A water sulfonic (50:50% v/v) acid 11 26.04 Ethanol 2   187 139.25  50 50 N/A 12 26.44 Methanol 2.1 132 200.30  75 50 N/A 13 25.74 Acetone  2.95 400 64.35 N/A 75 N/A 14 26.18 Acetonitrile: Oxalic  2.99 130 201.38  25 50 N/A water acid (50:50% v/v) 15 26.61 Ethanol  2.98 187 142.30  50 50 N/A 16 25.81 Methanol  2.86 132 195.53  75 50 N/A

TABLE 8 Experimental Details for Primary Salt Screening Further solvent system added Further Solvent either to solvent system dissolve Solvent system Mass of Mass of added Initial or to system added to Input Solvent/ counter- to input concen- make for improve Sample material solvent Counter- ion (mg material tration slurry counter- mixing ID (mg) system ion or μL) (μL) (mg/mL) (μL) ion (μL) (μL) 17 25.36 Acetone L-  4.69 400 63.40 N/A 75 N/A 18 26.29 Acetonitrile: Tartaric  4.87 130 202.23  25 50 100 water acid (50:50%) v/v 19 25.05 Ethanol  4.66 187 133.96  50 50 100 20 25.4  Methanol 4.8 132 192.42  75 50 100 21 26.2  Acetone Fumaric  3.96 400 65.50 NA 75 N/A 22 25.26 Acetonitrile: Acid  3.67 130 194.31  25 50 N/A water (50:50%) v/v 23 25.22 Ethanol  3.69 187 134.87  50 50 N/A 24 25.34 Methanol  3.62 132 191.97  75 50 N/A 25 26   Acetone Benzoic  3.88 400 65.00 N/A 75 100 28 26.49 Acetonitrile: acid  4.09 130 203.77  25 50 N/A water (50:50%) v/v 27 25.27 Ethanol  3.78 187 135.13  50 50 N/A 28 25.23 Methanol  3.86 132 191.14  75 50 N/A 29 25.2  Acetone Succinic  3.67 400 63.00 N/A 75 100 30 25.75 Acetonitrile: acid  3.86 130 198.08  25 50 N/A water (50:50%) v/v 31 25.24 Ethanol  3.61 187 134.97  50 50 100 32 26.43 Methanol  3.88 132 203.23  75 50 N/A

Example 2. Results Characterization of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH2 by XRPD, PLM, TG/DTA, DSC, GVS, KF and HPLC-UV.

Characteristics:

-   -   predominantly amorphous by XRPD analysis.     -   non-birefringent by PLM analysis, with no clearly defined         morphology.     -   TG analysis showed a weight loss of ca. 2.79% from the outset up         to ca. 144° C., followed by weight loss of ca. 0.72%         corresponding to an endothermic event in the DTA at an onset of         ca. 144.3° C. (peak at ca. 155.2° C.).     -   DSC analysis showed a broad endothermic event from the outset up         to ca. 140° C., likely due to unbound solvent/water. A second         endotherm was observed at an onset of ca. 140.2° C. (peak at         155.6° C.).     -   GVS analysis of the indicated that         Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂, is highly hygroscopic, with a         mass increase of ca. 10% between 40-90% RH observed. The         post-GVS sample was also found to be predominantly amorphous by         XRPD.     -   contained ca. 3.61% water by KF analysis.     -   purity of 97.50% by HPLC analysis.

Approximate Solubility Assessment of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂

The solubility assessment was estimated by a solvent addition technique, heating at 50° C. between aliquots (see Table 9). The following observations and results were obtained:

-   -   excellent solubility in methanol, trifluoroethanol,         acetonitrile:water (50:50% v/v) and DMSO:acetone (50:50% v/v)         giving solubility values of ≥200 mg/mL.     -   Solubility values of ca. 140 mg/mL in ethanol and ca. 100 mg/mL         in 2-propanol:water (50:50% v/v) and ethanol:water (50:50% v/v)         were also observed.     -   Moderate solubility (ca. 58 to 24 mg/mL) was obtained in         acetone:water (50:50 v/v), methanol:water (50:50 v/v), and         DMSO:water (50:50 v/v).     -   Poor solubility (≤17 mg/mL) was obtained in all other solvent         systems investigated, including acetone, dichloromethane,         2-butanol, 2-propanol, methyl ethyl ketone, toluene, THF, ethyl         acetate and acetonitrile.     -   XRPD analysis was carried out on residual solids from some of         the solvent systems showing poor solubility, after slurrying at         50° C. overnight, with diffractograms of residual solids being         predominantly amorphous.

TABLE 9 Approximate Solubility Screen Results Approximate Solubility Solvent (50° C.)/mg/mL Acetone <10 Ethanol 140 Methanol 200 2-Propanol 14 2-Butanol 17 Methyl ethyl ketone <10 Dichloromethane* <10 Toluene <10 Acetone:water (50:50% v/v) 58 Ethanol:water (50:50% v/v) 100 Methanol:water (50:50% v/v) 45 2-propanol:water (50:50% v/v) 100 Tetrahydrofuran <10 Ethyl acetate <10 Acetonitrile <10 Trifluoroethanol >200 Acetonitrile:water(50:50% v/v) 200 DMSO:acetone(50:50% v/v) 400 DMSO:water(50:50% v/v) 24 *35° C. for dichloromethane

Small-Scale Crystallization Trials

Cooling/Temperature Cycling Crystallizations

Small-scale temperature cycling crystallization trials using Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ were carried out in 7 different solvent systems, using ethanol, methanol, trifluoroethanol, acetone:water (50:50% v/v, Acetonitrile:water (50:50% v/v) and DMSO:water (80;20% v/v). The following results and observations were obtained from these experiments:

-   -   Clear solutions were observed in all of the experiments at 50°         C.     -   Within 1 hour of granulation at 50° C., nucleation followed by         crystallization was observed in experiments using methanol at         both concentrations of ca. 100 mg/mL and 150 mg/mL.     -   Observations and results are summarized in Table 10.     -   XRPD analysis showed crystallization of the material from         experiments using methanol as a solvent.     -   PLM analysis of the dried, crystalline solids from methanol (ca.         100 mg/mL and 150 mg/mL concentration) indicated that the         material was birefringent with no well-defined morphology.     -   TG/DT analysis of the dried material isolated from methanol (100         mg/mL) showed a weight loss of ca. 1.39% from the outset up to         ca. 168° C. An endothermic event at an onset of 168.5° C. (peak         at 175.9° C.) followed by degradation of the material was         observed in the DTA.     -   HPLC analysis of the dried material isolated from acetone:water         (50:50% v/v) and ethanol indicated a purity value of 98.80% and         98.81% respectively.     -   HPLC analysis of the dried crystalline material isolated from         methanol using concentrations of ca. 150 mg/mL and ca. 100 mg/mL         indicated purity values of 98.24% and 98.62% respectively.

TABLE 10 Observations and Results from Cooling/Temperature Cycling Crystallizations Observation Solvent/ after Sample solvent Observation temperature ID system at 50° C. cycling XRPD 1 Acetone:water Clear solution Slurry Predominantly (50:50% v/v) amorphous 2 Ethanol Clear solution Gel-like Predominantly amorphous 3 Methanol Clear solution Very thick Crystalline slurry 4 Methanol Clear solution Slurry Crystalline 5 Trifluoro- Clear solution Clear ethanol solution 6 Aceto- Clear solution Gel-like nitrile:water thin slurry (50:50% v/v) 7 DMSO:water Clear solution Clear (80:20% v/v) solution

Anti-Solvent Addition/Cooling/Temperature Cycling Crystallizations

Small-scale cooling followed temperature cycling produced crystalline material using methanol as a solvent. In order to investigate further solvent systems for crystallization of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂, cooling/temperature cycling crystallizations were carried out using methanol, ethanol and trifluoroethanol as the solvents and using acetonitrile, ethyl acetate, THF, acetone, MEK, toluene and heptane as the anti-solvents. The following results and observations were obtained from these experiments:

-   -   After temperature cycling, a slurry was observed for experiments         using methanol/anti-solvent mixtures.     -   Thick precipitation was observed after temperature cycling for         most of the experiments using ethanol/anti-solvent and         trifluoroethanol/anti-solvent mixtures.     -   The wet material isolated from methanol/anti-solvent mixtures         was free flowing but the wet material from ethanol/anti-solvents         and trifluoroethanol/anti-solvents was gel-like.     -   Observations and results are summarized in Table 11 and Table 12         respectively.     -   XRPD analysis on the isolated material indicated that         crystalline material was produced from methanol/anti-solvent         mixtures and poorly crystalline to partially crystalline         material from ethanol/anti-solvent mixtures and         trifluoroethanol/anti-solvent mixtures.

TABLE 11 Observations from Anti-solvent Addition Cooling/Temperature Cycling Crystallizations Observation Observation at 50° C., after % after temperature Observation Sample Anti- % Anti- addition of cycling before ID Solvent solvent Solvent solvent anti-solvent (at 5° C.) isolation  1 Methanol Acetonitrile 73.7 26.3 Clear Slurry Slurry solution  2 Methanol EA 73.7 26.3 Clear Slurry Slurry solution  3 Methanol THF 73.7 26.3 Clear Slurry Slurry solution  4 Methanol Acetone 73.7 26.3 Clear Slurry Slurry solution  5 Methanol MEK 73.7 26.3 Clear Slurry Slurry solution  6 Methanol Toluene 73.7 26.3 Clear Thin Thin solution Slurry Slurry  7 Methanol Heptane 73.7 26.3 Clear Slurry Slurry solution  8 Ethanol EA 74.4 25.6 Precipitation Thick Slurry precipitation  9 Ethanol THF 74.4 25.6 Clear/slight Thick Slurry turbid precipitation 10 Ethanol Acetone 74.4 25.6 Clear Thick Thin solution slurry slurry 11 Ethanol MEK 74.4 25.6 Slight Thick Slurry turbid precipitation 12 Ethanol Toluene 74.4 25.6 Clear Thick Slurry solution precipitation 13 Ethanol Heptane 74.4 25.6 Turbid Thick Slurry precipitation 14 Ethanol TBME 74.4 25.6 Thin Thick Slurry slurry precipitation 15 Ethanol Acetonitrile 74.4 25.6 Clear Slurry Thin solution slurry 16 Trifluoroethanol EA 50.0 50.0 Thick Thick Slurry precipitation precipitation 17 Trifluoroethanol THF 50.0 50.0 Thick Thick Slurry precipitation precipitation 18 Trifluoroethanol Acetone 50.0 50.0 Thick Thick Slurry precipitation precipitation 19 Trifluoroethanol MEK 50.0 50.0 Slurry Thick Slurry precipitation 20 Trifluoroethanol Toluene 50.0 50.0 Clear Clear Clear solution solution solution 21 Trifluoroethanol Heptane 50.0 50.0 Slight Slight Slight turbid turbid Turbid 22 Trifluoroethanol TBME 50.0 50.0 Thick Thick slurry Slurry precipitation 23 Trifluoroethanol Acetonitrile 50.0 50.0 Thick Thick Slurry precipitation precipitation

TABLE 12 Results from Anti-solvent Addition Cooling/Temperature Cycling Crystallizations Purity Solvent/ % by Sample solvent Anti- % anti- XRPD HPLC ID system solvent Solvent solvent analysis (%)  1 Methanol Acetonitrile 73.4 26.6 Crystalline 97.86  2 Methanol EA 73.7 26.3 Crystalline 98.19  3 Methanol THF 73.7 26.3 Crystalline 96.43  4 Methanol Acetone 73.7 26.3 Crystalline 97.86  5 Methanol MEK 73.7 26.3 Crystalline 97.88  6 Methanol Toluene 73.7 26.3 Crystalline 97.46  7 Methanol Heptane 73.7 26.3 Crystalline 97.70  8 Ethanol EA 74.4 25.6 Poorly 98.01 crystalline  9 Ethanol THF 74.4 25.6 Poorly 96.69 crystalline 10 Ethanol Acetone 74.4 25.6 Partially 98.59 crystalline 11 Ethanol MEK 74.4 25.6 Partially 98.31 crystalline 12 Ethanol Toluene 74.4 25.6 Partially 98.03 crystalline 13 Ethanol Heptane 74.4 25.6 Partially 98.11 crystalline 14 Ethanol TBME 74.4 25.6 Partially 97.87 crystalline 15 Ethanol Acetonitrile 74.4 25.6 Partially 98.66 crystalline 16 Trifluoroethanol EA 50.0 50.0 Partially 97.10 crystalline 17 Trifluoroethanol THF 50.0 50.0 Partially 97.41 crystallite 18 Trifluoroethanol Acetone 50.0 50.0 Poorly 97.31 crystalline 19 Trifluoroethanol MEK 50.0 50.0 Poorly 97.99 crystalline 20 Trifluoroethanol Toluene 50.0 50.0 21 Trifluoroethanol Heptane 50.0 50.0 22 Trifluoroethanol TBME 50.0 50.0 Poorly 97.71 crystalline 23 Trifluoroethanol Acetonitrile 50.0 50.0 Poorly 97.47 crystalline

Anti-Solvent Addition Crystallizations

Further anti-solvent addition crystallizations were carried out using methanol and ethanol as the solvents with anti-solvents (75% v/v) added at 50° C. and 5° C. The anti-solvents used were acetonitrile, ethyl acetate, THF, acetone, MEK, toluene, TBME and heptane. The following results and observations were obtained from these experiments:

-   -   The wet material isolated from methanol/anti-solvent mixtures         was free flowing but the wet material from ethanol/anti-solvents         and trifluoroethanol/anti-solvents was gel like.     -   Observations and results are summarized in Table 13 and Table 14         respectively.     -   XRPD analysis on the isolated material revealed that crystalline         material was produced from methanol/anti-solvent mixtures except         from the methanol/toluene mixture at 50° C. where a partially         crystalline material was observed. Predominantly amorphous to         partially crystalline material was produced from         ethanol/anti-solvent mixtures.

TABLE 13 Observations from Cooling/Temperature Cycling Crystallizations using Solvent/Anti-solvent Mixtures Observation Observations Solvent/ % after Anti- at 5° C. (after Sample solvent Anti- Temp- % anti- Observation solvent temperature ID system solvent erature Solvent solvent at 50° C. addition cycling)  1 Methanol Acetonitrile 50° C. 25 75 Clear Clear solution Thick solution followed slurry by slow crystallization  2 EA 25 75 Clear Clear solution Thick solution followed slurry by slow crystallization  3 THF 25 75 Clear Clear Slurry solution solution (very slow crystallization)  4 Acetone 25 75 Clear Clear solution Thick solution followed slurry by slow crystallization  5 MEK 25 75 Clear Clear solution Thick solution followed slurry by slow crystallization  6 Toluene 25 75 Clear Clear solution Thick solution followed slurry by slow crystallization  7 TBME 25 75 Clear Clear solution Thick solution followed slurry by slow crystallization  8 Ethanol Acetonitrile 50° C. 25 75 Clear Clear Thick slurry solution solution (Gel like)  9 EA 25 75 Clear Clear Thick slurry solution solution (Gel like) 10 THF 25 75 Clear Clear Slurry solution solution (Gel like) 11 Acetone 25 75 Clear Clear Thick slurry solution solution (Gel like) 12 MEK 25 75 Clear Clear Pale yellow solution solution slurry (Gel like) 13 Toluene 25 75 Clear Clear Thick slurry solution solution (Gel like) 14 TBME 25 75 Clear Precipitation- Thick slurry solution Gel like (Gel like) 15 Heptane 25 75 Clear Turbid Thick slurry solution (Gel like) 16 Methanol Acetonitrile  5° C. 25 75 Slurry Thick Thick slurry precipitation 17 EA 25 75 Slurry Thick Slurry slurry 18 THF 25 75 Slurry Thick Slurry precipitation 19 Acetone 25 75 Slurry Thick Slurry precipitation 20 MEK 25 75 Slurry Thick Slurry precipitation 21 Toluene 25 75 Slurry Thick Slurry slurry 22 TBME 25 75 Slurry Thick Slurry slurry 23 Ethanol Acetonitrile  5° C. 25 75 Turbid Thick Slurry precipitation 24 EA 25 75 Slight Thick Slurry Turbid precipitation 25 THF 25 75 Slight Thick Thin Turbid precipitation slurry 26 Acetone 25 75 Slight Thick Thin Turbid precipitation slurry 27 MEK 25 75 Slight Thick Thin Turbid precipitation slurry 28 Toluene 25 75 Slight Thick Very thin Turbid precipitation slurry 29 TBME 25 75 Slight Thick Thin Turbid precipitation slurry 30 Heptane 25 75 Slight Thick Thin Turbid precipitation slurry

TABLE 14 Results from Cooling/Temperature Cycling Crystallizations using Solvent/Anti-solvent Mixtures % Sample Anti- % anti- HPLC ID Solvent solvent Temperature Solvent solvent XRPD %  1 Methanol Acetonitrile 50° C. 25.0 75.0 Crystalline 96.94  2 EA 25.0 75.0 Crystalline 97.26  3 THF 25.0 75.0 Crystalline 98.85  4 Acetone 25.0 75.0 Crystalline 97.49  5 MEK 25.0 75.0 Crystallite 97.81  6 Toluene 25.0 75.0 Partially 98.01 crystalline  7 TBME 25.0 75.0 Crystalline 97.35  8 Ethanol Acetonitrile 50° C. 25.0 75.0 Crystalline 98.32  9 EA 25.0 75.0 Partially 96.76 crystalline 10 THF 25.0 75.0 Poorly 95.94 crystalline 11 Acetone 25.0 75.0 Partially 98.87 Crystalline 12 MEK 25.0 75.0 Predominantly 97.49 amorphous 13 Toluene 25.0 75.0 Predominantly 97.08 amorphous 14 TBME 25.0 75.0 Partially 98.81 crystalline 15 Heptane 25.0 75.0 Predominantly 97.44 amorphous 16 Methanol Acetonitrile  5° C. 25 75 Crystalline 97.6  17 EA 25 75 Crystalline 97.55 18 THF 25 75 Crystalline 97.57 19 Acetone 25 75 Crystalline 97.55 20 MEK 25 75 Crystalline 97.42 21 Toluene 25 75 Crystalline 97.30 22 TBME 25 75 Crystalline 97.12 23 Ethanol Acetonitrile  5° C. 25 75 Partially 98.95 crystalline 24 EA 25 75 Partially 98.02 crystalline 25 THF 25 75 Partially 97.85 crystalline 26 Acetone 25 75 Partially 98.42 crystalline 27 MEK 25 75 Partially 98.52 crystalline 28 Toluene 25 75 Predominantly 97.42 amorphous 29 TBME 25 75 Partially 98.51 crystalline 30 Heptane 25 75 Partially 97.44 crystalline

Seeded Cooling Crystallization Using Solvent/Anti-Solvent Mixtures

Crystalline Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ was previously obtained from methanol and methanol/anti-solvent mixtures by cooling/temperature cycling crystallizations. The same crystalline form was observed and was designated as Form 1. Seeded cooling crystallizations of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ using solvent/anti-solvent mixtures were carried out, where crystallizations were seeded using Form 1 at 50° C. followed by a slow cool to 5° C. The following results and observations were obtained from these experiments:

-   -   After seeding with Form 1 at 50° C., seed persisted and further         nucleation was observed during granulation at 50° C. in every         experiment.     -   At 5° C., a thick slurry was observed.     -   The material isolated from methanol/anti-solvent mixtures was         free flowing. Ethanol/anti-solvents produced gel-like material         and after drying this material was observed to be partially         glass-like.     -   Observations and results are summarized in Table 15 and Table 16         respectively.     -   XRPD analysis on the isolated material revealed that crystalline         material was produced from methanol/anti-solvent mixtures.         Partially crystalline material was observed from         ethanol/anti-solvent mixtures

TABLE 15 Observations from Seeded Cooling Crystallizations using Solvent/Anti-solvent Mixtures Observations Obser- after % anti- vations after granulation Obser- Obser- Anti- solvent/ Observ- Anti-solvent for 1 hour at vations at vations Sample solvent/ % co- ations addition at 50° C. (after 5° C. before ID Solvent co-solvent Solvent solvent at 50° C. 50° C. seeding) (cooling) isolation 1 Methanol Acetone 75 25 Clear Clear Thin slurry- Thick Slurry solution solution crystallization slurry 2 Methanol 2-propanol 75 25 Clear Clear Thin slurry- Thick Slurry solution solution crystallization slurry 3 Methanol 2-butanol 75 25 Clear Clear Thin slurry- Thick Slurry solution solution crystallization precipitation 4 Methanol TBME 75 25 Clear Clear Thin slurry- Thick Slurry solution solution crystallization precipitation 5 Methanol Ethanol 50 50 Clear Clear Thin slurry- Thick Slurry solution solution crystallization slurry 6 Ethanol 2-propanol 75 25 Clear Clear Thin slurry- Thick Slurry solution solution crystallization precipitation 7 Ethanol 2-butanol 75 25 Clear Clear Thin slurry- Thick Slurry solution solution crystallization precipitation

TABLE 16 Results from Seeded Cooling Crystallizations using Solvent/Anti-solvent Mixtures Anti- % anti- Observations Sample solvent/co- % solvent/co- before HPLC ID Solvent solvent Solvent solvent Isolation XPRD (%) 1 Methanol Acetone 75 25 Slurry Crystalline 97.81 2 Methanol 2-propanol 75 25 Slurry Crystalline 97.95 3 Methanol 2-butanol 75 25 Slurry Crystalline 98.27 4 Methanol TBME 75 25 Slurry Crystalline 98.27 5 Methanol Ethanol 50 50 Slurry Crystalline 97.69 6 Ethanol 2-propanol 75 25 Slurry Partially 97.72 crystalline 7 Ethanol 2-butanol 75 25 Slurry Partially 97.58 crystalline

Scale-Up Seeded Cooling Crystallizations Using Solvent/Anti-Solvent Mixtures

Crystallization scale-up experiments were carried out with Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ on a ca. 250 mg scale, using methanol, methanol/acetonitrile, methanol/THF and ethanol/acetone solvent systems. The following results and observations were obtained from these experiments:

-   -   After seeding at 50° C., seed persisted and further nucleation         was observed during granulation at 50° C. for every experiment.     -   At 5° C., either a thick slurry or freely stirrable slurry was         observed.     -   The material isolated from methanol and methanol/anti-solvent         mixtures was free flowing, the ethanol/acetone solvent system         produced a gel-like material and after drying the material was         observed to be partially glass-like.     -   Observations and results are summarized in Table 17 and Table 18         respectively.         Methanol (100 mg/mL)     -   XRPD analysis on the isolated material showed that crystalline         material was produced.     -   PLM analysis of the dried material indicated that the material         was birefringent with no well-defined morphology.     -   TG/DTA showed a weight loss of ca. 1.97% from the outset up to         ca. 169° C. An endothermic event was observed at an onset of         169.2° C. (peak at 178.7° C.) in the DTA.     -   The experiment produced crystalline material with a 85.06%         theoretical yield.     -   HPLC analysis on the dried material showed an uplift in purity         from 97.5% (purity of input material) to 98.5%.         Methanol:Acetonitrile (75:25% v/v)     -   XRPD analysis on the isolated material showed that crystalline         material was produced.     -   PLM analysis of the dried material indicated that the material         was birefringent with no welldefined morphology.     -   TG/DTA showed a weight loss of ca. 2.0% from the outset up to         ca. 170° C. An endothermic event was observed at an onset of ca.         170.9° C. (peak at 180° C.) in the DTA.     -   The experiment produced crystalline material with a 88.97%         theoretical yield.     -   HPLC analysis on the dried material showed an uplift in purity         from 97.5% (purity of input material) to 98.6%.         Methanol:THF (25:75% v/v)     -   XRPD analysis on the isolated material showed that crystalline         material was produced.     -   PLM analysis of the dried material indicated that the material         was birefringent with no well-defined morphology.     -   TG/DTA showed a weight loss of ca. 1.79% from the outset up to         ca. 165° C. An endothermic event was observed at an onset of         165.2° C. (peak at 173.1° C.) in the DTA.     -   The experiment produced crystalline material with a 31.57%         theoretical yield.     -   HPLC analysis on the dried material showed an uplift in purity         from 97.5% (purity of input material) to 99.2%.         Ethanol:Acetone (25:75% v/v)     -   XRPD analysis on the isolated material showed that predominantly         amorphous material was produced.     -   PLM analysis of the dried material indicated that the material         was non-birefringent.     -   TG/DTA showed a weight loss of ca. 1.3% from the outset up to         ca. 144° C. An endothermic event was observed at an onset of         144.6° C. (peak at 153.4° C.) in the DTA. TG/DTA was observed to         be similar to input Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂,         predominantly amorphous material.     -   The experiment produced predominantly amorphous material with a         84.39% theoretical yield.     -   HPLC analysis on the dried material showed an uplift in purity         from 97.5% (purity of input material) to 98.4%.

TABLE 17 Observations from Scale-up Seeded Cooling Crystallizations Observations Observation Observations after at 50° C. after granulation before addition of for 1 hour at Sample Anti- Anti- addition of anti solvent 50° C. (after Observations ID Solvent solvent Solvent solvent anti-solvent at 50° C. seeding) at 5° C. 1 Methanol 100.00  Clear N/A Thin slurry- Thick solution crystallization Slurry 2 Methanol Acetonitrile 75.00 25.00 Clear Clear Thin slurry- Thick solution solution crystallization Slurry 3 Methanol THF 25.00 75.00 Clear Clear Thin slurry- Slurry solution solution crystallization 4 Ethanol Acetone 25.00 75.00 Clear Clear Thin slurry- Slurry (Gel- solution solution crystallization like material)

TABLE 18 Results from Scale-up Seeded Cooling Crystallizations Mean Mean Purity % Conc. In Solid Area Mother Sample Anti- Purity (Mother Liquor Theoretical ID Solvent solvent XRPD % Area Liquor) mg/mL yield (%) 1 Methanol Crystalline 98.51 97.69 94.94 85.06 2 Methanol Acetonitrile Crystalline 98.63 97.66 91.93 88.97 3 Methanol THF Crystalline 99.24 98.98 38.97 31.57 4 Ethanol Acetone Predominantly 98.44 96.48 10.38 84.39 amorphous

Primary Salt Screening

A limited salt screen was carried out on Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ with the aim of locating crystalline salts in order to assess the potential for purification through salt formation.

Salt screening on Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ was carried out using hydrochloric acid, p-toluenesulfonic acid, methane sulfonic acid, oxalic acid, L-tartaric acid, fumaric acid, benzoic acid and succinic acid using acetone, acetonitrile:water (50:50% v/v), ethanol and methanol as solvent systems. The following results and observations were obtained from these experiments:

Salt Formation Using Hydrochloric Acid

-   -   After temperature cycling, gel-like material was observed when         using acetone, acetonitrile:water (50:50% v/v) and ethanol. A         slurry was observed when using methanol as the solvent.     -   XRPD analysis on the isolated material showed that crystalline         material (Form 1, free base) was produced from methanol and         predominantly amorphous material was produced from the acetone,         acetonitrile:water (50:50% v/v) and ethanol solvent systems.

Salt Formation Using p-Toluene Sulfonic Acid

-   -   After temperature cycling, a clear solution with some solids at         the bottom of the vial was observed using acetone as the         solvent. Gel-like material was observed using acetonitrile:water         (50:50% v/v), a slurry was observed using methanol and a clear         solution was produced using ethanol.     -   XRPD analysis on the isolated material showed that partially         crystalline material having an XRPD pattern different from the         free base Form 1 was produced from acetone and         acetonitrile:water (50:50% v/v). Partially crystalline material,         having some peaks in common with the free base Form 1 was         observed from methanol.

Salt Formation Using Methane Sulfonic Acid

-   -   After temperature cycling, a slurry was observed using acetone         and ethanol, gel-like material was observed using         acetonitrile:water (50:50% v/v) and a clear solution was         produced from methanol as the solvent.     -   XRPD analysis on the isolated material showed that partially         crystalline material having an XRPD pattern different from free         base Form 1 was produced from acetone and acetonitrile:water         (50:50% v/v). Predominantly amorphous material was observed from         ethanol.

Salt Formation Using Oxalic Acid

-   -   After temperature cycling, a gel-like material was observed         using acetonitrile:water (50:50% v/v) and ethanol. A slurry was         observed when using acetone and methanol as the solvents.     -   XRPD analysis on the isolated material revealed that crystalline         material (Free base, Form 1) was produced from methanol,         predominantly amorphous material was produced from ethanol and a         partially crystalline material having an XRPD pattern different         from free base Form 1 was produced from acetonitrile:water         (50:50% v/v). Crystalline material having an XRPD pattern         different from free base Form 1 was observed from acetone.

Salt Formation Using L-Tartaric Acid

-   -   After temperature cycling, a slurry was observed when using         acetone and methanol, whilst a gel-like material was observed         when using acetonitrile:water (50:50% v/v) and ethanol.     -   XRPD analysis on the isolated material revealed that crystalline         material (Free base, Form 1) was produced from methanol and         predominantly amorphous material was produced form acetone and         ethanol. Partially crystalline material having an XRPD pattern         different from free base Form 1 was produced from         acetonitrile:water (50:50% v/v).

Salt Formation Using Fumaric Acid

-   -   After temperature cycling, a slurry was observed when using         acetone and methanol, whilst a gel-like material was observed         when using acetonitrile:water (50:50% v/v) and ethanol.     -   XRPD analysis on the isolated material showed that crystalline         material (Free base, Form 1) was produced from methanol and         predominantly amorphous material was produced form acetone and         ethanol. Partially crystalline material having an XRPD pattern         different from the free base Form 1 was produced from         acetonitrile:water (50:50% v/v).

Salt Formation Using Benzoic Acid

-   -   After temperature cycling, gel-like material was observed using         acetonitrile:water (50:50% v/v) and ethanol. A slurry was         observed when using acetone as the solvent. Solid was observed         from methanol.     -   XRPD analysis on the isolated material revealed that poorly         crystalline material (Free base, Form 1) was produced from         acetone and ethanol. Crystalline material (slightly different         from free base Form 1) was produced from acetonitrile:water         (50:50% v/v) and methanol.

Salt formation using Succinic acid

-   -   After temperature cycling, a gel-like material was observed when         using acetonitrile:water (50:50% v/v) and a slurry was observed         when using ethanol or methanol as the solvent.     -   Solid was observed from acetone.     -   XRPD analysis on the isolated material showed that partially         crystalline material (Free base, Form 1) was produced from         acetone, ethanol and methanol. Poorly crystalline material         (slightly different from free base Form 1) was produced from         acetonitrile:water (50:50% v/v).         Observations are summarized in Table 19 and Table 20 and results         are summarized in Table 21 and Table 22.

TABLE 19 Observations from Primary Salt Screening Observation Observation before after Observation Observation addition of addition of after after Solvent/ Initial counterion counterion temperature temperature Sample solvent observations solution/slurry solution at cycle (16 cycling (40 ID system Counterion at 50° C. at 50° C. 50° C. hours) hours)  1 Acetone HC1 Slurry Slurry Slurry Gel like Gel like  2 Acetonitrile: Clear Clear Slurry Gel like Gel like water solution solution (50:50% v/v) followed by precipitation: slurry  3 Ethanol Clear Turbid Clear Gel like Gel like solution solution followed by precipitation: slurry  4 Methanol Clear Slurry Slurry Slurry Slurry solution followed by precipitation: slurry  5 Acetone P-toluene Slurry Slurry Clear Clear Clear sulfonic solution solution/ solution/ acid some solids some solids at the bottom at the bottom  6 Acetonitrile: Clear Clear Turbid Gel like Gel like water solution solution (50:50% v/v) followed by precipitation: slurry  7 Ethanol Clear Slurry Clear Clear Clear solution solution solution solution followed by precipitation: slurry  8 Methanol Clear Slurry Slurry Slurry Slurry solution followed by precipitation: slurry  9 Acetone Methane Slurry Slurry Slurry Slurry Slurry 10 Acetonitrile: sulfonic Clear Slurry Clear Gel like Gel like water acid solution solution (50:50% v/v) followed by precipitation: slurry 11 Ethanol Clear Turbid Slight Slurry Slurry solution Turbid followed by precipitation: slurry 12 Methanol Clear Slurry Clear Clear Clear solution solution solution solution followed by precipitation: slurry 13 Acetone Oxalic Slurry Slurry Slurry Slurry Slurry 14 Acetonitrile: Acid Clear Clear Clear Gel like Gel like water solution solution solution (50:50% v/v) followed by precipitation: slurry 15 Ethanol Clear Turbid Slurry Gel like Gel like solution followed by precipitation: slurry 16 Methanol Clear Slurry Slurry Slurry Slurry solution followed by precipitation: slurry

TABLE 20 Observations from Primary Salt Screening Observation Observation before after Observation Observation addition of addition of after after Solvent/ Initial counterion counterion temperature temperature Sample solvent observations solution/slurry solution at cycle (16 cycling (40 ID system Counterion at 50° C. at 50° C. 50° C. hours) hours) 17 Acetone L- Slurry Slurry Slurry Slurry Slurry 18 Acetonitrile: Tartaric Clear Slurry Slurry Gel like Gel like water Acid solution (50:50% v/v) followed by precipitation: slurry 19 Ethanol Clear Slurry Slurry Gel like Gel like solution followed by precipitation: slurry 20 Methanol Clear Slurry Slurry Slurry Slurry solution followed by precipitation: slurry 21 Acetone Fumaric Slurry Slurry Slurry Slurry Slurry 22 Acetonitrile: Acid Clear Clear Clear Gel like Gel like water solution solution solution (50:50% v/v) followed by precipitation: slurry 23 Ethanol Clear Turbid Clear Gel like Gel like solution solution followed by precipitation: slurry 24 Methanol Clear Slurry Slurry Slurry Slurry solution followed by precipitation: slurry 25 Acetone Benzoic Slurry Slurry Slurry Slurry Slurry 26 Acetonitrile: Acid Clear Clear Clear Gel like Gel like water solution solution solution (50:50% v/v) followed by precipitation: slurry 27 Ethanol Clear Turbid Clear Gel like Gel like solution solution followed by precipitation: slurry 28 Methanol Clear Slurry Slurry Solid Dry solid solution followed by precipitation: slurry 29 Acetone Succinic Slurry Slurry Slurry Solid Dry solid 30 Acetonitrile: Acid Clear Turbid Clear Gel like Gel like water solution solution (50:50% v/v) followed by precipitation: slurry 31 Ethanol Clear Turbid Slurry Slurry Slurry solution followed by precipitation: slurry 32 Methanol Clear Slurry Slurry Slurry Slurry solution followed by precipitation: slurry

TABLE 21 Results from Primary Salt Screening Sample Solvent/Solvent % Purity ID system Counterion XRPD by HPLC 1 Acetone HCl Predominantly Amorphous (Same as input material) 2 Acetonitrile:water Poorly Crystalline (slightly 97.94 (50:50% v/v) different than input material) 3 Ethanol Predominantly Amorphous (Same as input material) 4 Methanol Crystalline, same form as crystalline free material 5 Acetone P-toluene Partially crystalline 99.25 sulfonic acid (different form from crystalline free material) 6 Acetonitrile:water Poorly Crystalline (slightly 89.97 (50:50% v/v) different than input material) 7 Ethanol 8 Methanol Partially crystalline (some peaks matching with the crystalline free material) 9 Acetone Methane Partially crystalline 84.44 sulfonic acid (different form from crystalline free material) 10 Acetonitrile:water Poorly Crystalline (slightly (50:50% v/v) different than input material) 11 Ethanol Predominantly Amorphous (slightly different than input material) 12 Methanol 13 Acetone Oxalic Acid Crystalline (different form 98.02 from crystalline free material) 14 Acetonitrile:water Poorly Crystalline (slightly 87.29 (50:50% v/v) different than input material) 15 Ethanol Predominantly Amorphous (Same as input material) 16 Methanol Crystalline, same form as crystalline free material

TABLE 22 Results from Primary Salt Screening Sample Solvent/Solvent % Purity ID system Counterion XRPD by HPLC 17 Acetone L-Tartaric Predominantly amorphous acid (slightly different than input material) 18 Acetonitrile:water Poorly crystalline (slightly 98.64 (50:50% v/v) different than input material) 19 Ethanol Poorly crystalline (slightly different than input material) 20 Methanol Crystalline, same form as crystalline free material 21 Acetone Fumaric Predominantly amorphous (same acid as input material) 22 Acetonitrile:water Poorly crystalline (slightly 98.65 (50:50% v/v) different than input material) 23 Ethanol Predominantly amorphous (mixture of input free material and crystalline free material) 24 Methanol Crystalline, same form as crystalline free material 25 Acetone Benzoic Poorly crystalline (similar to acid crystalline free material) 26 Acetonitrile: water Crystalline (slightly different 98.71 (50:50%v/v) from crystalline free material) 27 Ethanol Poorly crystalline, similar form as crystalline free material) 28 Methanol Crystalline (slightly different 98.97 than crystalline free material) 29 Acetone Succinic Partially crystalline (mixture acid of input free material and crystalline free material) 30 Acetonitrile:water Poorly crystalline (slightly 98.68 (50:50% v/v) different than input material) 31 Ethanol Partially crystalline, same form as crystalline free material 32 Methanol Partially crystalline, same form as crystalline free material

Summary of Results

Initial characterization of Boc-D-Arg-DMT-Lys (Boc)-Phe-NH2, showed it to be predominantly amorphous by XRPD analysis and non-birefringent by PLM analysis, exhibiting no clearly defined morphology. TG/DT analysis showed a weight loss of ca. 2.79% from the outset up to ca. 144° C., followed by a weight loss of ca. 0.72%, associated with an endothermic event at ca. 144.3° C. (onset ca. 155.2° C.). DSC analysis showed a broad endothermic event from the outset up to ca. 140° C. with a further endothermic event observed at ca. 155.6° C. (onset at ca. 140.2° C.). KF analysis indicated a water content of ca. 3.61%, while GVS analysis indicated the material was highly hygroscopic, with a mass increase of ca. 10% from 40-90% RH. The purity of the received material was 97.50% by HPLC.

An approximate solvent solubility screen was carried out using 19 solvent systems and yielded a range of solubilities. The received material was found to be highly soluble, with methanol, trifluoroethanol, acetonitrile:water (50:50% v/v) and DMSO:acetone (50:50% v/v) giving solubility values of ≥200 mg/mL. A solubility of ca. 140 mg/mL was obtained in ethanol with a ca. 100 mg/mL solubility observed in 2-propanol:water (50:50% v/v) and ethanol:water (50:50% v/v). Moderate solubility (ca. 58 to 24 mg/mL) was observed in acetone:water (50:50 v/v), methanol:water (50:50 v/v), and DMSO:water (50:50 v/v), with poor solubility (≤17 mg/mL) obtained in all other solvent systems investigated, including acetone, dichloromethane, 2-butanol, 2-propanol, methyl ethyl ketone, toluene, THF, ethyl acetate and acetonitrile. The residual solids from some of the solvent systems showing poor solubility were analyzed by XRPD after slurrying at 50° C. overnight, but all diffractograms indicated that the material remained predominantly amorphous.

Small-scale crystallization screening experiments were carried out investigating cooling, temperature cycling, anti-solvent addition and seeding techniques. Cooling followed by temperature cycling crystallizations were carried out using seven different initial solvent mixtures. The material was dissolved in ethanol, methanol, trifluoroethanol, acetone:water (50:50% v/v, Acetonitrile:water (50:50% v/v) and DMSO:water (80:20% v/v) at 50° C. The solutions were cooled down to 5° C. then temperature cycled between 40° C. and 5° C. Crystallization of material at 50° C. was observed with methanol at both the process concentrations of 150 mg/mL and 100 mg/mL and crystalline material was isolated (Form 1) which was birefringent by PLM analysis, with no defined morphology. The purity of the solid isolated from methanol was 98.24% (ca. 150 mg/mL) and 98.62% (ca. 100 mg/mL), indicating that crystallization offered purity uplift over the input predominantly amorphous material. Predominantly amorphous solids were isolated from ethanol and acetone:water (50:50% v/v) showing purity values of 98.80% and 98.81%, indicating a purity uplift over the input material, however the wet material isolated from these solvent systems was gel-like. The other solvent systems did not yield solids.

Anti-solvent addition followed by cooling/temperature cycling crystallizations were carried out using 23 solvent/anti-solvent mixtures. The material was dissolved in ethanol, methanol, and trifluoroethanol at 50° C. Anti-solvents acetonitrile, ethyl acetate, THF, acetone, MEK, toluene, heptane and TBME (for ethanol and trifluoroethanol) were added at 50° C. to achieve ratios of methanol/anti-solvent (73.7:26.3% v/v), ethanol/anti-solvent (74.4:25.6% v/v) and trifluoroethanol/anti-solvent (50:50% v/v). Clear solutions were observed at 50° C. with methanol/anti-solvents but for ethanol/anti-solvent mixtures and trifluoroethanol/anti-solvent mixtures for most experiments turbidity to thick precipitation was observed. The crystallizations were cooled down to 5° C. then temperature cycled between 40° C. and 5° C. Crystalline material was isolated from methanol/antisolvent mixtures (Form 1). The purity values of the solids isolated from methanol/anti-solvent mixtures were between 96.43% and 98.19%, indicating that the crystallization offered a purity uplift for some of the methanol/anti-solvent mixtures. Poorly crystalline to partially crystalline solids were isolated from ethanol/anti-solvent mixtures and trifluoroethanol/anti-solvent mixtures. Purity of the solids was between 96.69% and 98.66%, but the wet material isolated from these solvent systems was gel-like.

Further anti-solvent addition crystallizations were carried out using 15 solvent/anti-solvent mixtures. The material was dissolved in methanol and ethanol at 50° C. Anti-solvents acetonitrile, ethyl acetate, THF, acetone, MEK, toluene, TBME and heptane (for ethanol) were added at 50° C. and 5° C. to achieve solvent/anti-solvent ratios of (25:75% v/v). Crystalline material was isolated from methanol/anti-solvent mixtures except from the methanol/toluene mixture at 50° C., where partially crystalline material was observed. The maximum uplift of purity was observed from methanol/THF (THF addition at 50° C.) where a purity of 98.85% was afforded. Predominantly amorphous to partially crystalline material was produced from ethanol/anti-solvent mixtures with a maximum uplift of purity (98.95%) observed from ethanol/acetonitrile (acetonitrile addition at 5° C.). The wet material isolated from ethanol/anti-solvent mixtures was however gel-like.

Seeded anti-solvent addition crystallizations using solvent/anti-solvent mixtures were carried out in 7 solvent systems. For methanol/anti-solvent mixtures (75:25% v/v), acetone, 2-propanol, 2-butanol, TBME were used as the anti-solvents and a methanol/ethanol (50:50% v/v) ratio was also used. For ethanol/anti-solvent mixtures (75:25% v/v), 2 propanol and 2-butanol were used as the anti-solvents. The material was dissolved in methanol and ethanol at 50° C. Anti-solvents were added at 50° C., affording clear solutions. The clear solutions were seeded with Form 1 at 50° C. followed by granulation for 1 hour where crystallization was observed. The crystallizations were cooled down to 5° C. Crystalline material was isolated from methanol/anti-solvent mixtures and partially crystalline material from ethanol/anti-solvent mixtures. The maximum uplift in purity was observed using methanol/2-butanol and methanol/TBME, showing a purity of 98.27% for both solvent systems.

The seeded anti-solvent addition cooling crystallizations were further scaled up to 250 mg scale using methanol (100 mg/mL), methanol/acetonitrile (75:25% v/v), methanol/THF (25:75% v/v) and ethanol/acetone (25:75% v/v) solvent systems. Crystalline material was isolated from methanol and methanol/anti-solvent mixtures and predominantly amorphous material from the ethanol/acetone system. The best result was obtained from methanol/acetonitrile with a theoretical yield of 88.97% and a purity of 98.63%. A purity of 99.24% was obtained from methanol/THF (25:75% v/v), but the theoretical yield was only 31%. The predominantly amorphous material obtained from ethanol/acetone (25:75% v/v) showed a purity of 98.44% with a theoretical yield of 84.39%.

A limited salt screen was carried out on Boc-D-Arg-DMT-Lys(Boc)-Phe-NH2 with the aim of locating a crystalline salt and assessing potential purification through salt formation. The counter ions and solvent systems used for the salt screening included hydrochloric acid, p-toluenesulfonic acid, methane sulfonic acid, oxalic acid, L-tartaric acid fumaric acid, benzoic acid and succinic acid in acetone, acetonitrile:water (50:50% v/v), ethanol and methanol. The material was slurried/dissolved in the solvent systems at 50° C. In acetone, slurries were observed but in the remaining systems, clear solutions were obtained. Within 1 hour of granulation at 50° C., crystallization of material was observed and a slurry was present for every experiment. The experiments were further diluted with the respective solvent system to dissolve the crystallized material or to afford a stirrable slurry. The counterion solutions were added to the respective experiments at 50° C. The experiments were stirred at 50° C. and cooled down to 5° C. and then temperature cycled between 5° C. to 40° C. for ca. 40 hours.

Salt screening using Hydrochloric acid produced predominantly amorphous to poorly crystalline gel-like material, having a diffractogram slightly different from the input material in acetone, acetonitrile:water (50:50% v/v) and ethanol. Crystalline material (Form1, free base) was observed using methanol as the solvent.

Salt screening using p-Toluene sulfonic acid produced partially crystalline material having an XRPD pattern different from the free base Form 1 in acetone. ¹H NMR analysis on the solids revealed salt formation and a purity of 99.25% was observed. Poorly crystalline gel-like material having a diffractogram slightly different from the input material was observed from acetonitrile:water (50:50% v/v) with a purity of 89.97%. Methanol produced partially crystalline material similar to the crystalline free base.

Salt screening using Methane sulfonic acid produced partially crystalline material having an XRPD pattern different from the free base Form 1 in acetone with a purity of 84.44%. Poorly crystalline and predominantly amorphous gel-like material having a diffractogram slightly different from the input material was observed from acetonitrile:water (50:50% v/v) and ethanol respectively.

Salt screening using Oxalic acid produced crystalline material having a XRPD pattern different from the crystalline free base Form 1 in acetone, with a purity of 98.02%. ¹H NMR analysis on the solids indicated salt formation. Poorly crystalline gel-like material having a diffractogram slightly different from the input material was observed from acetonitrile:water (50:50% v/v) with a purity of 87.29%. No salt formation was observed using ethanol and methanol as solvents as these systems produced material having diffractograms identical to the input material and crystalline free base respectively.

Salt screening using L-Tartaric acid produced predominantly amorphous and poorly crystalline material having an XRPD pattern slightly different from the input material in acetone, acetonitrile:water (50:50% v/v) and ethanol respectively. Poorly crystalline material produced from acetonitrile:water (50:50% v/v) showed a purity of 98.64%. Crystalline free base Form 1 was produced from methanol.

Salt screening using Fumaric acid produced predominantly amorphous material having an XRPD pattern similar to the amorphous input and a pattern showing a mixture of crystalline and amorphous free base from acetone and ethanol respectively. Poorly crystalline material produced from acetonitrile:water (50:50% v/v) showed a purity of 98.65%. Crystalline free base Form 1 was produced from methanol.

Salt screening using Benzoic acid produced poorly crystalline material having an XRPD pattern similar to crystalline free base Form 1 from acetone and ethanol. Crystalline material having an XRPD pattern slightly different from crystalline free base Form 1 was produced from acetonitrile:water (50:50% v/v) and methanol with purities of 98.71% and 98.87% respectively.

Salt screening using Succinic acid produced partially crystalline material similar to crystalline form 1 was observed from acetone, ethanol and methanol. Poorly crystalline material produced from acetonitrile:water (50:50% v/v) showed a purity of 98.68%.

Overall, the crystallization screening study on Boc-D-Arg-DMT-Lys (Boc)-Phe-NH₂ indicated that crystalline material could be obtained by re-crystallization of the predominantly amorphous solid in methanol and methanol/anti-solvent mixtures. An uplift in purity was observed through crystallization of the intermediate. The primary salt screening study on Boc-D-Arg-DMT-Lys (Boc)-Phe-NH₂ resulted in crystalline material from oxalic acid in acetone having a different XRPD pattern compared with free base Form 1. Partially crystalline material having an XRPD pattern different from the free base Form 1 was obtained from p-toluene sulfonic acid in acetone. Further work would be required in order to better ascertain the nature of these solid forms

Overall, crystalline material could be obtained by re-crystallization of the predominantly amorphous solid in methanol and in methanol/anti-solvent mixtures. The crystalline material was successfully produced at a 250 mg scale using methanol (100 mg/mL), methanol/acetonitrile (75:25% v/v) and methanol/THF (25:75% v/v). Using methanol/acetonitrile (75:25% v/v) we obtained a yield of 88.97% and purity of 98.63%. Limited salt screening resulted in crystalline and partially crystalline material when using oxalic acid and p-Toluenesulfonic acid in acetone, respectively. Both of the materials showed XRPD diffractgrams different from the crystalline free base Form 1. These salt formations also offered purity uplifts over the input material with a purity of 98.02% from the oxalic acid experiment and 99.25% from the p-Toluenesulfonic acid experiment.

The approximate solvent solubility screen utilized nineteen solvent systems and yielded a range of solubilities. The received material was found to be highly soluble, with methanol, trifluoroethanol, acetonitrile:water (50:50% v/v) and DMSO:acetone (50:50% v/v) giving solubility values of ≥200 mg/mL. A solubility of ca. 140 mg/mL was obtained in ethanol with a ca. 100 mg/mL solubility observed in 2-propanol:water (50:50% v/v) and ethanol:water (50:50% v/v). Moderate solubility (ca. 58 to 24 mg/mL) was obtained in acetone:water (50:50 v/v), methanol:water (50:50 v/v) and DMSO:water (50:50 v/v), with poor solubility (≤17 mg/mL) obtained in all other solvent systems investigated. The screen identified acetone, dichloromethane, 2-butanol, 2-propanol, methyl ethyl ketone, toluene, THF, ethyl acetate and acetonitrile as potential anti-solvents.

Small-scale crystallization screening experiments were carried out investigating cooling, temperature cycling, anti-solvent addition and seeding techniques. Cooling/temperature cycling crystallizations using methanol (at process concentrations of 150 mg/mL and 100 mg/mL) yielded crystalline material which were birefringent by PLM analysis, with no defined morphology. The purity of the crystallized solids isolated from methanol was 98.24% (ca. 150 mg/mL) and 98.62% (ca. 100 mg/mL), indicating that crystallization offered a purity uplift over the input predominantly amorphous material (97.5%). Crystallized wet material from acetone:water (50:50% v/v) and ethanol was gel-like and after drying, glass-like material was observed. Using water as part of the crystallization solvent was observed to be unsuitable for production of crystalline material, but ethanol was further investigated. Anti-solvent addition/cooling/temperature cycling crystallizations using methanol/anti-solvents (73:27% v.v) also produced crystalline material (Form 1). Ethanol/anti-solvents (74:46% v/v) and trifluoroethanol/anti-solvents (50:50% v/v) produced gel-like material which was observed to be poorly crystalline to partially crystalline, but an uplift in purity over the input material was observed with some of these solvent systems. Anti-solvent addition crystallizations, where anti-solvents (75% v/v) were added at 50° C. and 5° C. produced crystalline material using methanol/anti-solvent mixtures at both temperatures. Ethanol/anti-solvent (25:75% v/v) mixtures again produced gel-like material which dried to a glass-like solid. Seeded cooling crystallizations resulted in crystalline material from methanol/anti-solvent mixtures and partially crystalline material from ethanol/anti-solvent mixtures. When ethanol was used along with methanol (50:50% v/v), crystalline material was observed, however the use of ethanol along with other solvents did not allow for crystallization. An uplift in purity over the input material was observed with a maximum uplift of purity using methanol/2-butanol and methanol/TBME, where both experiments showed purities of 98.27%.

The seeded anti-solvent addition cooling crystallizations were further scaled up to 250 mg scale using methanol (100 mg/mL), methanol/Acetonitrile (75:25% v/v), methanol/THF (25:75% v/v) and ethanol/acetone (25:75% v/v). Crystalline material was isolated from methanol and methanol/anti-solvent mixtures and predominantly amorphous material from ethanol/acetone system. Using methanol/acetonitrile we obtained a yield of 88.97% and purity of 98.63%. A purity of 99.24% was obtained from methanol/THF (25:75% v/v), but the yield was only 31%. The predominantly amorphous material obtained from ethanol/acetone (25:75% v/v) showed a purity of 98.44% with a yield of 84.39%.

Limited salt screening was carried out on Boc-D-Arg-DMT-Lys(Boc)-Phe-NH2, with the aim of locating a crystalline salt and assessing potential purification through salt formation. The screen entailed the use of hydrochloric acid, p-toluenesulfonic acid, methane sulfonic acid, oxalic acid, L-tartaric acid, fumaric acid, benzoic acid and succinic acid as the counterions in acetone, acetonitrile:water (50:50% v/v), ethanol and methanol solvent systems. Limited success was seen from the salt screen with crystalline material produced from oxalic acid in acetone and partially crystalline material from p-Toluene sulfonic acid in acetone, both having different XRPD patterns compared with the crystalline free base Form 1. All other salt formation reactions resulted in predominantly amorphous, poorly crystalline, partially crystalline and crystalline material having XRPD patterns similar to or only slightly different from the amorphous received material or crystalline free base.

Crystallization of the Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ intermediate material did not show an improvement in terms of hygroscopicity, but it did allow for purification.

Example 3. HCI-IPA Deprotection of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂

Equipment: A 1 L 3-neck round-bottomed flask equipped with a mechanical stirrer, thermometer, addition funnel and a nitrogen inlet.

Procedures:

-   -   Charge Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ (35.4 g. 0.042 mol, 1.0         eq).     -   Charge IPA (280 mL, 8 parts) and begin agitation.     -   Adjust temperature to 22° C. (19-25° C.).     -   Charge 5-6 M HCl in IPA (77 mL, 0.42 mol, 10.0 eq) over a period         of 10 minutes while maintaining temperature below 25° C.     -   Adjust temperature to 40-45° C.     -   Agitate mixture at 40-45° C. for a period of 1-2 h.     -   A sample of the mixture (ca. 0.5 mL) is removed for IPC #3         testing. Analytical methods and typical results are provided in         the appropriate sections below.     -   IPC #3 is used to determine reaction completion as indicated by         the disappearance of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ by UPLC.         Limit: Report only, % a/a.     -   Typical results for IPC #3: Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ wrt         (Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂+D-Arg-DMT-Lys-Phe-NH₂)=ND.     -   Cool suspension to 22° C. (19-25° C.) over a period of 1-2 h.     -   Filter suspension.     -   Wash solids with IPA (3×70 mL, 3×2 parts).     -   Dry on filter under a stream of N₂ at room temperature for a         minimum of 17 h to give a white solid.     -   Unload the filter and weigh D-Arg-DMT-Lys-Phe-NH₂ solid.     -   Typical mass is 30.7 g, uncorrected for solvent.     -   A sample of the solid (ca. 250 mg) is removed for IPC #4         testing. Analytical methods and typical results are provided in         the appropriate sections below.     -   IPC #4a is used to determine residual IPA by GC. Limit: Report         only, ppm.     -   Typical result for IPC #5a: IPA=4.4% w/w.     -   IPC #4b is used to determine purity of C745 by HPLC. Limit:         Report only, % a/a.     -   Typical result for IPC #5b: C745 purity=98.41% a/a.     -   Charge crude C789 to the reactor (30.7 g, 1.0 eq).     -   Charge MTBE (460 mL, 15 parts wrt crude C745) and begin         agitation.     -   Charge EtOH (92 mL, 3 parts).     -   Adjust temperature to reflux (ca. 55° C.).     -   Agitate suspension at reflux temperature for a period of 16-18         h.     -   Adjust temperature to 22° C. (19-25° C.) over 1-2 h.     -   Agitate suspension at 22° C. (19-25° C.) for a period of 2-3 h.     -   Filter suspension.     -   Wash solids with MTBE (2×60 mL, 2×2 parts).     -   Dry on filter under a stream of N₂ at room temperature for a         minimum of 12 h to give a white solid.

This initial process using 5-6M HCl in IPA resulted in the formation of isopropyl ester analog as well as several t-butylated analogs as impurities.

This solid required treatment with EtOH-MTBE to remove the IPA that was trapped in the solid (presumably a solvate as drying at 100° C. for extended periods of time did reduce the level below a certain amount.

Although effective at removing the iPrOH and at reducing the iPr ester content, it resulted in the formation of the ethyl ester.

Example 4. Improved Deprotection of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂

A second procedure was developed using HCl in TFE with TIPS as a t-butyl cation scavenger. This procedure avoids the formation of alkyl esters but additionally reduced the number and amount of t-butylated analogs present.

To a cooled (0-5° C.) slurry of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂ (0.500 g, 0.570 mmol) and triisopropylsilane (0.584 mL, 2.85 mmol) in 2,2,2-trifluoroethanol (5.0 mL, 69 mmol) was added conc. hydrogen chloride (0.238 mL, 2.85 mmol) dropwise over approx. 5 min. After 10 min, the ice bath was removed and the mixture stirred at ambient temperature. After approx. 20 min at ambient temperature, all solids had dissolved leading to the formation of a biphasic mixture. After 1 h at ambient temperature HPLC analysis showed the consumption of Boc-D-Arg-DMT-Lys(Boc)-Phe-NH₂. The product purity was observed to be 98.13 area % [Agilent 1100 HPLC, Waters XSelect CSH C18, 150×4.6 mm, 3.5 micron, 1.0 ml/min, UV220 nm, Column temperature 30° C.; Solvent A: H2O (0.05% TFA); Solvent B: acetonitrile (0.05% TFA). Hold 1 min 95% A, 15 min gradient 95% to 80% A, 5 min 80% to 50% A, 5 min 50% to 10% A, hold 2 min at 10% A, 0.1 min gradient 10% to 95% A. Hold at 95% A for remainder of 36 min run time. Diluent 9:1 water/ACN]. An HPLC peak at a RRT of 1.04 was observed (0.9 area %). No TFE ester was observed by LCMS. After 90 min, the mixture was diluted with MeOAc (5 mL) affording a white precipitate. Volatiles were removed at reduced pressure and the solid concentrated from MeOAc (5 mL) to afford a free flowing white solid that was dried in vacuo overnight. Residual solvents observed by ¹H NMR included TFE (7% w/w) and MeOAc (0.3% w/w). Product purity was 98.08 area % as assayed by HPLC. The solid was slurried in MTBE/MeOAc (2:1, 10 ml) for 10 min at 40° C., cooled to ambient temperature, filtered and dried in vacuo in a lyophilization vessel immersed in a 60° C. oil bath overnight to afford the title compound [411 mg, 96% (uncorrected for residual solvents)] as a white solid. Final product purity by HPLC was 98.07 area %. Residual solvents observed by ¹H NMR included TFE (2.03% w/w) and MeOAc (0.19% w/w).

Example 5. XRPD Pattern of a Hydrochloride Salt of Compound I from Methanol:2-Propanol (75%:25% v/v)

TABLE A Pos. Height FWHM Left d-spacing Rel. Int. [°2θ] [cts] [°2θ] [Å] [%] 3.7579 3373.12 0.0768 23.51305 70.94 4.2659 4169.45 0.0895 20.71409 87.69 6.5526 917.62 0.0640 13.48938 19.30 7.2841 697.14 0.0895 12.13641 14.66 8.0800 85.65 0.0900 10.93359 1.80 8.5065 84.96 0.1535 10.39489 1.79 9.7875 1672.39 0.0895 9.03704 35.17 10.6288 355.31 0.0895 8.32361 7.47 12.0543 189.97 0.1535 7.34226 4.00 12.7809 419.79 0.1279 6.92643 8.83 13.3068 656.50 0.1151 6.65387 13.81 14.1827 1182.25 0.0895 6.24486 24.86 14.5619 1327.04 0.1279 6.08305 27.91 15.0219 487.99 0.1023 5.89783 10.26 16.1288 613.50 0.2303 5.49546 12.90 16.9425 569.74 0.1535 5.23331 11.98 18.0211 4755.00 0.1151 4.92245 100.00 18.7982 2930.95 0.1407 4.72068 61.64 19.1243 583.81 0.1023 4.64092 12.28 19.6849 749.80 0.1535 4.51001 15.77 20.1376 596.39 0.1535 4.40963 12.54 20.5047 887.59 0.1535 4.33150 18.67 20.9553 2520.28 0.1151 4.23938 53.00 22.0163 1124.72 0.0895 4.03740 23.65 22.6867 1684.20 0.1279 3.91959 35.42 23.2292 904.36 0.1407 3.82926 19.02 24.0145 846.12 0.2047 3.70580 17.79 24.5746 412.17 0.1791 3.62258 8.67 25.1662 582.42 0.1279 3.53876 12.25 25.9049 650.36 0.1279 3.43950 13.68 26.4986 307.14 0.2558 3.36377 6.46 27.4092 275.34 0.1535 3.25405 5.79 27.9577 182.83 0.2047 3.19144 3.85 29.2173 173.31 0.3070 3.05666 3.64 30.4972 145.70 0.1535 2.93123 3.06 30.9418 102.65 0.0900 2.88773 2.16 31.7727 126.66 0.3070 2.81642 2.66 32.2938 161.36 0.1535 2.77215 3.39 33.4213 63.17 0.3070 2.68116 1.33

Example 6. XRPD Pattern of a Hydrochloride Salt of Compound I from Methanol

TABLE B Pos. Height FWHM Left d-spacing Rel. Int. [°2θ] [cts] [°2θ] [Å] [%] 3.7036 1966.63 0.0640 23.85759 72.77 4.4432 2477.30 0.1023 19.88749 91.66 6.5634 704.32 0.0895 13.46726 26.06 7.4018 429.84 0.0512 11.94366 15.90 9.7210 1158.88 0.1023 9.09875 42.88 10.6210 224.51 0.1023 8.32964 8.31 11.0920 133.97 0.1535 7.97704 4.96 12.7331 103.83 0.0900 6.94660 3.84 13.1598 415.98 0.1023 6.72787 15.39 14.0930 454.88 0.1023 6.28439 16.83 14.7901 1040.30 0.0768 5.98973 38.49 16.7103 439.59 0.1535 5.30552 16.27 17.1509 141.83 0.0900 5.16593 5.25 18.0233 2702.62 0.1023 4.92186 100.00 18.5346 735.14 0.1023 4.78723 27.20 18.7979 1147.74 0.0640 4.72075 42.47 19.1239 789.29 0.0895 4.64101 29.20 19.5235 306.83 0.0900 4.54315 11.35 19.8085 422.15 0.1023 4.48213 15.62 20.1544 324.59 0.1535 4.40598 12.01 20.6070 478.45 0.1023 4.31022 17.70 20.8573 1011.67 0.0640 4.25907 37.43 21.3109 537.54 0.1535 4.16942 19.89 22.0189 619.33 0.2303 4.03694 22.92 22.6758 1060.70 0.1023 3.92146 39.25 23.0757 398.04 0.1535 3.85439 14.73 23.6744 38.83 0.0900 3.75515 1.44 23.9728 340.14 0.1791 3.71215 12.59 24.4777 293.52 0.1535 3.63671 10.86 25.7316 132.83 0.0900 3.45941 4.91 26.4407 215.92 0.2047 3.37100 7.99 27.7972 173.31 0.1791 3.20950 6.41 30.1162 99.20 0.2047 2.96744 3.67 32.1646 67.76 0.3070 2.78299 2.51

Example 7. XRPD Pattern of a Tosylate Salt of Compound I from Acetone

TABLE C Pos. Height FWHM d-spacing Rel. Int. [°2Th.] [cts] [°2Th.] [Å] [%] 5.1621 2149.15 0.1663 17.11956 100.00 8.9359 438.04 0.2303 9.89635 20.38 10.7664 184.28 0.2047 8.21754 8.57 13.3445 266.11 0.2047 6.63517 12.38 14.3884 539.35 0.4605 6.15602 25.10 15.9863 161.64 0.2558 5.54412 7.52 17.2952 407.57 0.2558 5.12739 18.96 18.8443 420.10 0.2047 4.70925 19.55 19.5521 362.22 0.1535 4.54033 16.85 21.0051 693.10 0.1535 4.22943 32.25 23.2998 206.42 0.3582 3.81783 9.60 24.6506 86.12 0.5117 3.61159 4.01

Example 8. XRPD Pattern of a Mesylate Salt of Compound I from Acetone

TABLE D Pos. Height FWHM d-spacing Rel. Int. [°2Th.] [cts] [°2Th.] [Å] [%] 5.4291 3079.02 0.0384 16.27808 100.00 8.0335 120.51 0.1535 11.00580 3.91 9.0773 115.67 0.2558 9.74250 3.76 10.8149 293.11 0.1279 8.18074 9.52 13.4288 415.08 0.1279 6.59369 13.48 14.7938 421.32 0.2558 5.98822 13.68 15.7960 318.03 0.1791 5.61049 10.33 17.5693 431.98 0.1535 5.04800 14.03 18.9795 376.14 0.1279 4.67599 12.22 19.6937 289.54 0.2047 4.50799 9.40 21.3056 720.36 0.2303 4.17044 23.40 22.2563 263.14 0.1535 3.99442 8.55 24.1299 237.45 0.7164 3.68833 7.71 25.7352 135.39 0.3070 3.46180 4.40 27.6495 84.81 0.4093 3.22631 2.75 30.9496 17.50 0.6140 2.88941 0.57

Example 9. XRPD Pattern of an Oxalate Salt of Compound I from Acetone

TABLE E Pos. Height FWHM Left d-spacing Rel. Int. [°2θ] [cts] [°2θ] [Å] [%] 4.0824 291.09 0.1023 21.64476 10.42 7.2188 323.51 0.1279 12.24600 11.58 7.7660 749.77 0.1023 11.38428 26.85 8.1685 455.55 0.0768 10.82427 16.31 8.7856 126.66 0.1023 10.06525 4.54 10.1057 979.70 0.0768 8.75327 35.08 11.7275 233.13 0.1023 7.54614 8.35 12.0519 307.19 0.1023 7.34374 11.00 12.2864 248.60 0.1023 7.20411 8.90 12.7774 846.47 0.1023 6.92837 30.31 13.2740 468.08 0.0768 6.67023 16.76 13.6796 175.54 0.1535 6.47336 6.29 14.4861 387.62 0.1151 6.11472 13.88 14.9214 326.40 0.1151 5.93732 11.69 15.1377 150.25 0.0900 5.84810 5.38 15.5347 106.18 0.0900 5.69954 3.80 16.1829 161.09 0.1535 5.47721 5.77 17.7646 1786.25 0.1151 4.99295 63.96 18.1548 399.21 0.1407 4.88652 14.30 18.5392 2792.57 0.0895 4.78604 100.00 18.9751 574.37 0.1023 4.67707 20.57 19.9095 1049.25 0.1023 4.45962 37.57 20.3639 672.05 0.1535 4.36113 24.07 21.0328 208.25 0.2047 4.22393 7.46 21.9414 400.27 0.0900 4.04767 14.33 21.9676 539.10 0.1023 4.04624 19.30 22.2732 718.09 0.1535 3.99141 25.71 22.8116 257.00 0.1535 3.89841 9.20 23.3197 −104.04 0.0900 3.81146 −3.73 23.5325 291.26 0.1279 3.78060 10.43 24.0190 147.43 0.1535 3.70511 5.28 24.8019 132.93 0.3070 3.58990 4.76 25.2913 145.65 0.2303 3.52153 5.22 25.6339 162.92 0.2047 3.47524 5.83 26.6566 202.58 0.2047 3.34419 7.25 27.7426 83.70 0.1535 3.21570 3.00 28.2705 228.59 0.1279 3.15684 8.19 28.9314 78.20 0.0900 3.08365 2.80 29.2563 124.89 0.2047 3.05267 4.47 30.0846 91.09 0.1535 2.97049 3.26 30.7947 123.92 0.2047 2.90359 4.44 31.5899 127.84 0.1535 2.83229 4.58 31.9371 93.79 0.0900 2.79997 3.36 32.8553 71.65 0.2047 2.72605 2.57

Example 10. XRPD Pattern of a Benzoate Salt of Compound I from Methanol

TABLE F Pos. Height FWHM Left d-spacing Rel. Int. [°2θ] [cts] [°2θ] [Å] [%] 3.6742 2073.90 0.0768 24.04811 100.00 4.4204 1347.38 0.0895 19.99017 64.97 6.7177 829.29 0.0768 13.15834 39.99 7.0320 229.18 0.0768 12.57092 11.05 8.2133 416.05 0.0895 10.76529 20.06 9.8583 662.53 0.0895 8.97235 31.95 10.2604 109.77 0.0900 8.61446 5.29 12.3942 500.02 0.1023 7.14170 24.11 13.2923 979.35 0.0895 6.66111 47.22 13.6972 1012.99 0.1023 6.46510 48.84 14.1013 1154.57 0.1023 6.28071 55.67 14.6960 340.34 0.2047 6.02788 16.41 15.7923 726.93 0.1023 5.61180 35.05 16.4926 394.77 0.1023 5.37505 19.04 17.0775 509.25 0.0768 5.19226 24.56 17.2537 552.89 0.1279 5.13961 26.66 18.0813 1729.49 0.1279 4.90621 83.39 18.4075 885.37 0.1279 4.81999 42.69 18.9537 1288.35 0.1279 4.68231 62.12 19.5451 747.42 0.1279 4.54194 36.04 19.7885 486.20 0.1023 4.48661 23.44 20.2166 505.95 0.1279 4.39256 24.40 20.6718 1051.62 0.1407 4.29685 50.71 20.8819 961.73 0.1279 4.25411 46.37 21.6381 545.53 0.1023 4.10712 26.30 22.2851 1623.89 0.1535 3.98930 78.30 22.6611 298.77 0.0900 3.92072 14.41 23.0749 506.06 0.1535 3.85453 24.40 24.3020 1218.36 0.1407 3.66260 58.75 24.7773 408.23 0.2047 3.59341 19.68 25.5656 337.24 0.2558 3.48437 16.26 26.6658 206.54 0.1535 3.34305 9.96 27.2542 199.90 0.2558 3.27220 9.64 27.7067 201.69 0.1535 3.21978 9.72 28.3209 285.54 0.2558 3.15134 13.77 29.3217 120.66 0.2047 3.04602 5.82 30.1348 153.42 0.4093 2.96566 7.40 30.4172 195.25 0.1535 2.93876 9.41 31.1772 176.27 0.3070 2.86884 8.50 32.4960 59.94 0.7164 2.75536 2.89 33.6018 144.00 0.1791 2.66717 6.94

INCORPORATION BY REFERENCE

All of the U.S. patents and U.S. and PCT published patent applications cited herein are hereby incorporated by reference.

EQUIVALENTS

The foregoing written specification is considered to be sufficient to enable one skilled in the art to practice the invention. The present invention is not to be limited in scope by examples provided, since the examples are intended as a single illustration of one aspect of the invention and other functionally equivalent embodiments are within the scope of the invention. Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and fall within the scope of the appended claims. The advantages and objects of the invention are not necessarily encompassed by each embodiment of the invention. 

1. A method of making Compound (II), the method comprising deprotecting compound (I),

or a salt thereof, thereby making compound (II)

or a salt thereof.
 2. The method of claim 1, wherein the step of deprotecting comprises: a. preparing a mixture of a crystalline form of Compound (I), triisopropylsilane, and 2,2,2-trifluoroethanol; and b. adding concentrated hydrochloric acid to the mixture.
 3. The method of claim 2, wherein the mixture is a slurry.
 4. The method of claim 2, wherein the crystalline form of Compound (I) is a crystalline form of a salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta as described in any one of Tables A′-F′ or shown in any one of FIGS. 9-14: wherein Table A′ is: Pos. [°2θ] 3.7579 4.2659 6.5526 7.2841 8.0800 8.5065 9.7875 10.6288 12.0543 12.7809 13.3068 14.1827 14.5619 15.0219 16.1288 16.9425 18.0211 18.7982 19.1243 19.6849 20.1376 20.5047 20.9553 22.0163 22.6867 23.2292 24.0145 24.5746 25.1662 25.9049 26.4986 27.4092 27.9577 29.2173 30.4972 30.9418 31.7727 32.2938 33.4213;

Table B′ is: Pos. [°2θ] 3.7036 4.4432 6.5634 7.4018 9.7210 10.6210 11.0920 12.7331 13.1598 14.0930 14.7901 16.7103 17.1509 18.0233 18.5346 18.7979 19.1239 19.5235 19.8085 20.1544 20.6070 20.8573 21.3109 22.0189 22.6758 23.0757 23.6744 23.9728 24.4777 25.7316 26.4407 27.7972 30.1162 32.1646;

Table C′ is: Pos. [°2θ] 5.1621 8.9359 10.7664 13.3445 14.3884 15.9863 17.2952 18.8443 19.5521 21.0051 23.2998 24.6506;

Table D′ is: Pos. [°2Th.] 5.4291 8.0335 9.0773 10.8149 13.4288 14.7938 15.7960 17.5693 18.9795 19.6937 21.3056 22.2563 24.1299 25.7352 27.6495 30.9496;

Table E′ is: Pos. [°2θ] 4.0824 7.2188 7.7660 8.1685 8.7856 10.1057 11.7275 12.0519 12.2864 12.7774 13.2740 13.6796 14.4861 14.9214 15.1377 15.5347 16.1829 17.7646 18.1548 18.5392 18.9751 19.9095 20.3639 21.0328 21.9414 21.9676 22.2732 22.8116 23.3197 23.5325 24.0190 24.8019 25.2913 25.6339 26.6566 27.7426 28.2705 28.9314 29.2563 30.0846 30.7947 31.5899 31.9371 32.8553;

Table F′ is: Pos. [°2θ] 3.6742 4.4204 6.7177 7.0320 8.2133 9.8583 10.2604 12.3942 13.2923 13.6972 14.1013 14.6960 15.7923 16.4926 17.0775 17.2537 18.0813 18.4075 18.9537 19.5451 19.7885 20.2166 20.6718 20.8819 21.6381 22.2851 22.6611 23.0749 24.3020 24.7773 25.5656 26.6658 27.2542 27.7067 28.3209 29.3217 30.1348 30.4172 31.1772 32.4960 33.6018;


5. The method of claim 2, wherein the crystalline form of Compound (I) is a crystalline form of a hydrochloride salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.8, 4.3, 9.8, 14.6, 18.0, 18.8, 20.9, and 22.7.
 6. The method of claim 5, wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.8, 4.3, 6.5, 7.3, 9.8, 13.3, 14.2, 14.6, 16.1, 16.9, 18.0, 18.8, 19.1, 19.7, 20.1, 20.5, 20.9, 22.0, 22.7, 23.2, 24.0, 25.2, and 25.9.
 7. The method of claim 2, wherein the crystalline form of Compound (I) is a crystalline form of a hydrochloride salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of 3.7, 4.4, 6.6, 9.7, 14.8, 18.0, 18.5, 18.8, 19.1, 20.9, and 22.7.
 8. The method of claim 7, wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.7, 4.4, 6.6, 7.4, 9.7, 10.6, 13.2, 14.1, 14.8, 16.7, 18.0, 18.5, 18.8, 19.1, 19.5, 19.8, 20.1, 20.6, 20.9, 21.3, 22.0, 22.7, 23.1, and 24.0.
 9. The method of claim 2, wherein the crystalline form of Compound (I) is a crystalline form of a tosylate salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 5.2, 8.9, 14.4, 17.3, 18.8, 19.5, and 21.0.
 10. The method of claim 9, wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 5.2, 8.9, 10.8, 13.4, 14.4, 16.0, 17.3, 18.8, 19.5, 21.0, 23.3, and 24.6.
 11. The method of claim 2, wherein the crystalline form of Compound (I) is a crystalline form of a mesylate salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 5.4, 13.4, 14.8, 15.8, 17.6, 19.0, and 21.3.
 12. The method of claim 11, wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 5.4, 10.8, 13.4, 14.8, 15.8, 17.6, 19.0, 19.7, 21.3, 22.3. 24.1, and 25.7.
 13. The method of claim 2, wherein the crystalline form of Compound (I) is a crystalline form of an oxalate salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 7.8, 10.1, 12.8, 17.8, 18.5, 19.9, and 22.3.
 14. The method of claim 13, wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 4.1, 7.2, 7.8, 8.1, 10.1, 12.0, 12.8, 13.3, 14.5, 14.9, 17.8, 18.1. 18.5, 19.9, 20.4, 21.9, 22.0, 22.3, and 23.5.
 15. The method of claim 2, wherein the crystalline form of Compound (I) is a crystalline form of a benzoate salt of Compound I and has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.7, 4.4, 14.1, 18.1, 18.9, 20.7, 22.3, and 24.3.
 16. The method of claim 15, wherein said crystalline form has characteristic peaks in its XRPD pattern at values of two theta (° 2θ) of: 3.7, 4.4, 6.7, 9.9, 13.3, 13.7, 14.1, 15.8, 17.2, 18.1, 18.4, 18.9, 19.5, 20.7, 20.9, 21.6, 22.3, and 24.3. 